It’s no secret that we are proponents of discovering consumer[1] wearable device data in personal injury litigation.[2] Although the subject is not new, there’s still “surprisingly little precedent”[3] on the issue. Wearable technology compiles extensive information on our movement, habits, and bodily systems. Fitness trackers and comprehensive smartwatches offer overlapping yet distinct health-tracking capabilities. Fitness trackers focus primarily on activity, exercise, sleep, and recovery tracking, while smartwatches provide a wider range of features including cellular connectivity and third-party apps. With AI, wearable technology can go so far as to monitor and predict diseases and chronic conditions. This data has obvious value in both the criminal[4] and civil[5] contexts.
In this article, we explore the utility of wearable device data and discuss how to pull back the curtain and admit this data before or during trial.
Wearable Witnesses
As a society, we love “gadgets.” And a wearable gadget? Sign. Us. Up. This has long been the case—calling back memories of Dick Tracy’s two-way wrist radio, Inspector Gadget’s video watch, James Bond’s laser-equipped watch, and the Spy Kids’ wrist communication, surveillance, and self-defense devices (which, by the end of the franchise, could “even tell time”). But even with this long-held interest in wearable tech, it wasn’t until 2009 that we saw the first modern(ish)-day wearable enter the actual market: The Fitbit.
The earliest Fitbit clipped on to its user and monitored sleep and activity by tracking steps, distance moved, calories burned, and active versus sedentary hours. It transferred data by syncing with a PC. The Fitbit continued to evolve, and by 2011, the wristwatch-style model Ultra had an altimeter, a digital clock, and a stopwatch. While rivaled by competitors, in 2014, Fitbit was reported to have secured 77 percent of the market for full-body activity trackers.[6] Not for long.
In 2015 came the Apple Watch: the first comprehensive smartwatch, equipped with a heart rate sensor, accelerometer, and gyroscope as well as the ability to make and receive calls.
Now, ten years into the wearables revolution, wrist-worn fitness trackers and comprehensive smartwatches are ubiquitous, as evidenced by the market’s surge in global sales. Generating approximately $12.67 billion in revenue in 2017, the market is projected to reach $32.05 billion this year, with a projected volume of $40.57 billion by 2029.[7]
We’ve seen Fitbit’s evolution as well as those of its long-time competitors (like Garmin). Other brands[8] have more recently entered the scene to capitalize on the market for wrist-worn, distraction-free tech, including those specifically designed with children[9] in mind. And now, fitness tracker “rings” are all the rage, monitoring and collecting data related to sleep, activity, stress, and wellness.[10] These trackers stand in comparison to comprehensive smartwatches. The Apple Watch Series 10 (WatchOS 11), for example, monitors heart rate, has an ECG app, provides fall and crash detection, tracks blood oxygen levels, monitors sleep patterns (including using an accelerometer to detect signs of sleep apnea), tracks sound exposure, and senses temperature.
Compatible applications can utilize various wearable devices and operating systems to detect and predict important health information. The Vitals app, for example, tracks overnight health metrics including heart rate, respiratory rate, wrist temperature, blood oxygen, and sleep duration and flags if certain metrics are abnormal, notifying users of outliers. The Parky and StrivePD apps are FDA cleared to track Parkinson’s disease symptoms, such as tremors and dyskinesia. Apps like Glucose Buddy help diabetic users manage their blood sugar, insulin dosages, and carbohydrate intake. These are merely examples of the countless health apps available to everyday consumers. And some apps facilitate communication and data sharing with users’ healthcare providers.[11]
With such advanced tracking, AI-powered coaching, predictive health warnings, and tracked collaboration between patients and healthcare providers, there is a wealth of data out there. This data can provide critical insight into a person’s health, wellness, activity, and—for our purposes—alleged injuries.
Discovering Wearable Device Data
The value of wearable device data in personal injury cases—for both parties—should be beyond dispute. But defendants have to get it before they can use it, and we have some ideas on how to do just that.[12]
Because wearable data relates directly to allegations in a personal injury complaint and is within the control of the device user, defense counsel should first insist that it is a form of “initial required disclosure” under Federal Rule of Civil Procedure 26(a)(1). To this end, we suggest initially requesting a litigation hold.[13] Next, defense counsel should propound written discovery requests that are narrowly tailored (both in scope and time), satisfying Rule 26(b)(1) proportionality requirements. We also recommend that defense counsel specify the medium by which they want the ESI data produced.[14] To piggy-back on written discovery requests, the topic of wearable device data should be explored during the plaintiff’s deposition, and, if appropriate, supplemental discovery should be sought.
Tracking Data from the User Into Court
As noted above, there is surprisingly little precedent on the discoverability of wearable device data. There’s even less on its admissibility. But earlier this year, the Supreme Court of Connecticut said, of course wearable data is admissible! We’re paraphrasing a little; the Court actually said: “[T]he trial court did not abuse its discretion in . . . finding the data from the [murder] victim’s Fitbit sufficiently reliable to be admissible scientific evidence.”[15]
So how to admit it? By demonstrating the touchstone requirements: relevance, authenticity, and reliability.
Relevance should be fairly straightforward. Data regarding a plaintiff’s activity levels may strengthen or weaken the claimed injury and damages. Because some wearables can measure emotional states or stress levels, there is potential to have this data admitted for claims of emotional and psychological injury, as well. But to the extent there’s any question as to relevance, we suggest citing examples of healthcare providers who use and rely on this data.
Cardiology is one area of medicine where the value and utilization of smartwatch data is on the rise. As one source aptly stated, the use of wearable devices “has the potential to broadly impact cardiovascular medicine through lifestyle modifications for primary prevention, arrhythmia screening of at-risk individuals, and remote management of patients with established heart failure (HF) or peripheral artery disease, among other chronic cardiovascular conditions.”[16] One study determined that Heart Rate Variability (“HRV”) metrics from a wearable device can identify COVID-19–related symptoms before it would have otherwise been diagnosed.[17] In a 2021 cross-sectional survey, 636 physicians were asked what they would do if a patient presented with no symptoms but had an Apple Watch alert for irregular heart rhythms.[18] While not relying on the devices’ notification alone, the providers were prompted by this data to make treatment decisions. In fact, the survey showed that in 99.5% of the cases, physicians opted for at least one diagnostic test, and in about 25%, physicians would consider prescribing medication.
The field of cardiology is, of course, just one example where healthcare providers see the relevance and value of wearable device data. In the clinical trial context, wearables are receiving attention across specialties. For example, smartwatch data was used in a recent Parkinson’s Disease clinical trial to assess users’ gait, tremor, finger tapping, and speech.[19] Studies have also shown that wearables can flag early signs of various health conditions and predict the results of simple blood tests.[20]
Simply put, if wearable data is relevant to providers in making healthcare decisions, it certainly ought to meet the legal threshold of relevance in any case where the plaintiff’s health and physical condition is at issue.
Having established relevance, the next step is to establish the data’s authenticity. One can do this in several ways.[21] Federal Rule of Evidence 901(b)(1) allows authentication through questioning the device-using plaintiff on the stand. That person appropriately qualifies as a witness with knowledge under the rule. Rule 901(b)(4) can also establish authenticity through distinctive features of the data—which may, for example, refer to a particular exercise type or location uniquely associated with the plaintiff, thus proving its tie to that individual. Rule 901(b)(9) could potentially allow evidence about the device’s data collection method and accuracy rate to be presented to establish authenticity. Finally, Rule 901(b)(3) allows for authentication through an expert who can verify the data’s origin. In discussing authenticity, the Connecticut Supreme Court opined that wearable device data could be properly “authenticated by someone with personal knowledge of authorship or personal knowledge of how that type of exhibit is routinely made.” It deemed the data admissible through the introduction of expert testimony about the operation and accuracy of the model at issue.[22]
Also to be confronted is the issue of reliability. Wearable devices sometimes erroneously track steps, for example, when a user travels by car. The proponent of this evidence can show that its data collection methods are sound by presenting evidence from the manufacturer or an expert regarding error rates or by collecting information on subsequent remedial measures taken to correct earlier malfunctions.
As a backstop, even if the raw data itself cannot be admitted, the proponent may still get its broad strokes admitted through the testimony of an expert witness, who need not rely on admissible evidence in preparing a report or testifying at trial.[23] A great way to get wearable device data before the jury may indeed be to have an expert rely on it as the basis for his or her expert opinion. Depending on the case, an expert witness could also rely on such data to establish that the plaintiff did not suffer from an alleged condition and discredit causation based on the physical metrics shown from the data (i.e., a plaintiff claiming a particular injury would not exhibit the physical data demonstrated from such metrics).
Conclusion
Defense counsel should seek to maximize the evidentiary value of wearable device data by strategically obtaining this data through discovery and laying the foundation for its admission at trial.
[1] The devices discussed are consumer devised, as opposed to prescribed devices (e.g., hearing aids, glucose monitors, heart monitors).
[2] See, e.g., Katelyn Ashton & Susanna Moldoveanu, The Wearable Witness: Utilizing Apple Watch Data in Civil Litigation, DRI For the Defense, October 2022, https://digitaleditions.walsworth.com/publication/?i=764267&article_id=4361412&view=articleBrowser.
[3] Bartis v. Biomet, Inc., No. 4:13-CV-00657-JAR, 2021 WL 2092785, at *2 (E.D. Mo. May 24, 2021) (“There is surprisingly little precedent on this issue given the ubiquitous presence of wearable devices.”); § 3:9. Wearable devices, 1 eDiscovery & Digital Evidence § 3:9 (“There is surprisingly little precedent on the issue of discoverability of electronically stored information on wearable technology, such as Fitbits.”); § 4:48. Wearable devices, Electronic Discovery and Records and Information Management Guide § 4:48 (stating the same); § 2:25. Wearable technology, Handbk. Fed. Civ. eDisc. & Records § 2:25 (4th ed.) (same).
[4] See, e.g.,Amanda Watts, Cops Use Murdered Woman’s Fitbit to Charge Her Husband, CNN (Apr. 26, 2017), https://edition.cnn.com/2017/04/25/us/fitbit-womans-death-investigation-trnd/index.html; Johnny Lieu, Police Use Apple Watch Health Data as Evidence in Murder Case, MASHABLE (Apr. 3, 2018), https://mashable.com/article/apple-watch-murder-case (victim’s Apple Watch activity and heart rate data used to establish the time of attack and death, thus implicating the murderer); Apple Health Data Used in Murder Trial, BBC (Jan. 2, 2018), https://www.bbc.com/news/technology-42663297 (using Apple Heath data and geo-data to support charges against an offender by establishing that he engaged in two periods of strenuous activity at the time of the victim’s rape and murder); Amanda Watts, Pacemaker Could Hold Key in Arson Case, CNN (Feb. 8, 2017), https://www.cnn.com/2017/02/08/us/pacemaker-arson—trnd/ (using pacemaker data to support arson charges, as the data refuted the user’s claim that he was asleep when the fire ensued); Jacob Gershman, Prosecutors Say Fitbit Device Exposed Fibbing in Rape Case, WSJ LAW BLOG (Apr. 21, 2016, 1:53 PM), https://www.wsj.com/articles/BL-LB-53611 (using Fitbit data to establish that an alleged victim had falsely reported a crime and was walking around at the time of her alleged assault).
[5] See, e.g., Parmy Olson, Fitbit Data Now Being Used in the Courtroom, Forbes (Nov. 16, 2014), http://onforb.es/1TSzwJJ (plaintiff using Fitbit data to show that her activity levels had decreased lower than is typical of someone her age and of her profession); Cory v. George Carden International Circus, Inc., No. 4:13-CV-760, 2016 WL 3460781, at *1 (E.D. Tex. Feb. 5, 2016) (compelling production of plaintiff’s “fitness monitoring accessories,” including “Fit Bits and running/walking GPS systems” as relevant to the plaintiff’s injury claims); Bartis v. Biomet, Inc., No. 4:13-CV-00657-JAR, 2021 WL 2092785, at *1 (E.D. Mo. May 24, 2021) (compelling production of the plaintiff’s Fitbit data in products liability suit against manufacturer of artificial hip, as such data was relevant to the plaintiff’s pain and limited mobility claims).
[6] Robert Hof, How Fitbit Survived As A Hardware Startup, Forbes (Feb. 4, 2014), https://www.forbes.com/sites/roberthof/2014/02/04/how-fitbit-survived-as-a-hardware-startup/#6b453c851934.
[7] Smartwatches – Worldwide, Statista, https://www.statista.com/outlook/hmo/digital-health/digital-fitness-well-being/fitness-trackers/smartwatches/worldwide (last visited July 9, 2025).
[8] See, e.g., WHOOP, https://www.whoop.com/us/en/ (last visited July 9, 2025) (citing celebrity users like Patrick Mahomes, Aly Raisman, Michael Phelps, and Rory McIlroy).
[9] Several companies design multiple models for children. See Rebecca Parsons & Constance Mahoney, The Best Kids’ Fitness Trackers of 2025, Gearjunkie(Nov. 27, 2024), https://gearjunkie.com/kids-gear/best-kids-fitness-trackers (reviewing kids’ fitness trackers from Fitbit, Garmin, Biggerfice, Kurio, MgaoLo); Ellen Lee, The Best Smartwatches for Kids, N.Y Times Wirecutter (June 5, 2025), https://www.nytimes.com/wirecutter/reviews/best-smartwatch-for-kids/ (discussing Apple Watch and Gizmo as options for kids).
[10] See, e.g., ŌURA, https://ouraring.com/?srsltid=AfmBOorbooT8qUYGGpQC3nsPl-IZu37KzFPmoCM92_2nDwZFVHnW2ttg (last visited July 9, 2025).
[11] For example, MyChart (Epic) is a patient portal that integrates with devices like Fitbit and Apple Health to share data such as weight, blood pressure, or steps walked in a day. Features: What You Can Do With MyChart, MyChart is Epic (last visited July 9, 2025), https://www.mychart.org/Features.
[12] See Ashton & Moldoveanu, supra note 2 (discussing the discoverability of smartwatch data).
[13] See Carol Michel & Rick Sager, Wearable Fitness Devices: A New Frontier in Discovery, LAW 360 (Mar. 28, 2016, 10:10 AM), https://www.law360.com/articles/775527/wearablefitness-devices-a-new-frontier-in-discovery.
[14] See Ashton & Moldoveanu, supra note 2 (discussing various methods of appropriate and acceptable production to avoid a ruling that producing such data is unduly burdensome on the plaintiff).
[15] State v. Dabate, 351 Conn. 428, 475–76 (2025).
[16] Andrew Hughes et al., Wearable Devices in Cardiovascular Medicine, 132:5 American Heart Association: Circulation Research 652 (March 2023), https://www.ahajournals.org/doi/epub/10.1161/ CIRCRESAHA.122.322389.
[17] Robert P. Hirten et al., Use of Physiological Data from a Wearable Device to Identify SARS-CoV-2 infection and Symptoms and Predict COVID-19 Diagnosis: Observational Study, Journal of Medical Internet Research (Feb. 2021), https://pubmed.ncbi.nlm.nih.gov/33529156/.
[18] Patrick C. Demkowicz et al., Physician Responses to Apple Watch-Detected Irregular Rhythm Alerts, Am. Heart J. (Aug. 2023), https://pubmed.ncbi.nlm.nih.gov/37084933/.
[19] Jamie L. Adams et al., Using a Smartwatch and Smartphone to Assess Early Parkinson’s Disease in the WATCH-PD Study Over 12 Months, npj Parkinsons Dis. (June 12, 2024), https://www.nature.com/articles/s41531-024-00721-2.
[20] See Hanae Armitage, Smartwatch Data Can Predict Blood Test Results, Study Reports, Stanford Med. (May 2021), https://med.stanford.edu/news/all-news/2021/05/smartwatch-data-can-predict-blood-test-results.html.
[21] See John G. Browning, Fitbit Data Brings Another Dimension to Evidence, IADC Committee Newsletter: TECHNOLOGY (July 2015), https://www.iadclaw.org/assets/1/19/Technology_July_2015.pdf.
[22] State v. Dabate, 351 Conn. 428, 474 (2025) (quoting Lorraine v. Markel American Ins. Co., 241 F.R.D. 534, 545 (D. Md. 2007)). Notably, the Court credited the expert’s testimony about his clinical research, which was funded through a grant from the NIH, to establish the accuracy of Fitbit devices, and, specifically, the model that the victim wore on the day of the murder. The expert is the director of the Wearable Device Reading Center at Columbia University Medical Center and spoke extensively about his research, describing the “validation study” and its finding that the Fitbit device is very accurate at measuring steps. In fact, it is more accurate than a research grade device (i.e., the Actical) at measuring both steps and energy expenditure. The expert also described the publication and peer review process that supported the validation study and explained his review of the many other published studies regarding the accuracy rate of the device.
[23] See United States v. Locascio, 6 F.3d 924, 938 (2d Cir. 1993) (“[T]he facts that form the basis for an expert’s opinions or inferences need not be admissible in evidence ‘[i]f of a type reasonably relied upon by experts in the particular field.’ . . . Thus, expert witnesses can testify to opinions based on hearsay or other inadmissible evidence if experts in the field reasonably rely on such evidence in forming their opinions.” (quoting Fed. R. Evid. 703)).
