Projects:2017s1-165 Forensic Investigation of Fitness Devices

Project Group Members

Sanjam Kohli

Yuan Li

Project Supervisor

Dr. Matthew Sorell

Introduction

High-tech wearable devices have always been objects of interest in science fiction. From cheap plastic activity bands or rudimentary watches, these gadgets have evolved into elegantly designed devices that can provide greater connectivity, location services, and more importantly, incredible insights into people’s health. These nifty instruments have the capability to monitor a consumer’s heart rate, sleep patterns, and even one’s blood oxygen levels. The smartwatch and fitness band market is dominated by global technology leaders Apple, Samsung, and FitBit. More than 50% of the Australians now own a smartwatch [1]. As these devices are being adopted by a growing number of users, there is an increasing potential for them to become a haven for digital evidence in criminal investigations.

Aim

The project aims to explore the use of wearable fitness devices as forensic evidence, and to establish movement and activities of victims or suspects involved in a homicide investigation. This was achieved by analysing the heart beat and activity records which can be extracted and analysed from the Apple Watch and a FitBit device or their respective paired phones.

Motivation and Significance

A victim’s time of death is crucial to every criminal investigation. Currently, it is extremely challenging to determine the time of death in a homicide investigation using conventional methods. The project attempts to develop a mechanism to establish a more accurate timeline of the incident and a precise time of death using the heart beat and activity logs extracted from fitness devices. The method devised could further assist the South Australian Police (SAPOL), and other law enforcing agencies in future investigations.

Technical Background

Determining the time of death

Estimating the time of death is very crucial to a homicide investigation. It is a critical element of the case timeline. A specific and accurate time of death can corroborate any statements given by suspects in a crime. Despite years of research by forensic experts, no conclusive method has been devised to estimate a victim’s time of death. Presently, the estimation is based on various case specific factors and pathological changes in the human body like changes in body temperature, muscle stiffness, and lividity. In the absence of any witnesses, the complexity of this process increases. By using the current methods, the time of death is usually placed within a range of hours. These processes are highly subjective to errors, and thus it is ‘utterly impossible’ to fix an exact time [2].

Resting and Active Calories

The Basal Metabolic Rate (BMR) is defined as the amount of energy (measured in kilojoules, kJ) burned at rest [3]. BMR is calculated using one’s biometrics like weight, height, age, and sex. Resting calories signify the caloric base burn rate, and are calculated by using the individual’s BMR. Active calories are the calories that are burned due to additional activity.

1 kilocalorie (kCal) = 4.184 kilojoules (kJ)

Total Energy (kJ) = Basal Energy (kJ) + Active Energy (kJ)

Calorie expenditure is relatively linear to heart rate for an average individual, provided that the individual’s heart rate remains within the safe range of 90-150bpm [4].

Biometrics

Biometrics is defined as the ‘the science and technology of analyzing biological data’ [15]. For the purpose of this project, the following biometrics are considered:

1. Heartrate (beats/min)

2. Steps (steps/min)

3. Total Energy (kJ) = Resting Energy (kJ) + Active Energy (kJ)

Apple Watch Series 1

Device Specifications

The specifications [5] for the Apple Watch used in this project are as follows:

1. 38mm (vertically)

2. 290ppi screen

3. Custom designed Apple S1 SiP (system in package) chip.

4. NFC +WiFi 802.11b’g’n + Bluetooth 4.0

5. 8 GB onboard storage

6. Sensors: Heart rate monitor, gyroscope, accelerometer

Photoplethysomography

The Apple Watch uses the concept of photoplethysomography (PPG) to measure the user’s heart rate [6]. The technology uses a simple principle of light absorption. The red color of the blood is due to the reflection of the red light, and the absorption of the green light. The Watch has infrared and green LED lights which are paired with light sensitive photodiodes (Fig 2.1). These lights are flashed at a high frequency (>400 Hz), to measure the blood flow in the user’s wrist. When the heart beats, there is an increase in the blood flow in the wrist, thus resulting in an increase in the rate of green light absorption, which is then measured by the photodiodes. The LED brightness and sampling rate can be adjusted automatically by the Watch in low signal level conditions.The heart rate data is transmitted to the Health app every 10 minutes on average through a stable Bluetooth or Wi-Fi connection. The data can then be compiled in a graph for users to study.

Steps Count

The Apple Watch has an accelerometer sensor which acts as a built-in step counter or pedometer. The steps are counted based on the height and stride length of the user.

Calorie Count

The Apple Watch measures the basal and active calories burnt using the biometrics (sex, weight, height) entered by the user, the user’s heart rate, and average human statistics. The activity being performed by the user is identified by the accelerometer, and is also considered for calculating energy expenditure.

Apple Watch memory and storage

The device consists of 512 MB of dynamic RAM, and 8 GB of flash memory. The Watch uses an HFS+ (hierarchical file system) created by Apple Inc., which has limited storage capacity than a device using removable SD cards

Device Syncing

The Apple Watch does not consist of a physical diagnostic port for users to transmit their data between devices. Thus, all the data is transferred and backed up in a companion iPhone by using either a Wi-Fi or Bluetooth connection. Once both the devices are in range, a stable ‘data stream’ is established. All the data is also backed up automatically in iCloud. The heart beat logs acquired by the Watch are sent to the paired iPhone. Using the built-in Health app, the user can access this data

FitBit Alta HR

Device Specifications

The hardware specifications of the device used for the project are as follow [9]:

1. 15mm wide

2. OLED tap display

3. Bluetooth 4.0

4. Sensors: Optical heart rate tracker, 3-axis accelerometer, vibration motor

5. Memory: 7 days of detailed data storage (minute by minute), daily summaries for 30 days

PurePulse

The PurePulse [10] is the continuous and automatic heart rate tracker used by FitBit. The sensor uses the principle of photoplethysomography, like the Apple Watch (Section 2.2.2). However, unlike the Apple Watch, the PurePulse sensor is capable of continuously monitoring the user’s heart rate during an activity and the resting heart rate too.

Step Count

FitBit consists of a 3-axis accelerometer which is used to detect motion. The sensor calculates the step count, distance, and calories burnt based on the duration, frequency, and intensity of the activity [13].

Calorie Count

FitBit considers the user’s biometrics like weight, age, height, and sex to determine the user’s BMR, and thereby calculate the energy expenditure based on the user’s activity.

Device Memory and Storage

The Alta HR can store detailed minute-by-minute data for up to 7 days in the device. Daily summaries can be stored for up to 30 days in the device if the data is not synced to cloud [9]. For investigative purposes, the device data needs to be exported within 4-5 days to ensure the details are preserved and data is not lost.

Device Syncing

The Alta HR uses Bluetooth Low Energy (LE) wireless technology and an internet connection (Wi-Fi/mobile data) to sync with mobile devices and computers. The device syncing range is up to 6.1 metres [9]. The device can also be synced with a computer using the dongle. If ‘All-day’ syncing is turned on, the devices should automatically sync every 15-30 minutes. Manual syncing is also available [14].