Table 1 Design considerations of the prototype mobility tracker

Hardware requirements

• The system should incorporate:

Passive radio-frequency identification (RFID) device or equivalent

o To accurately detect when the user leaves and arrives home.

o RFID reader should have algorithms to prevent false positives.

Global Positioning System (GPS) logger or equivalent

o To collect geospatial location and outdoor travel data every second.

o Accuracy of at least 10 m.

o Should be able to lock GPS position from cold start in less than 1 min.

o Should be able to record distance and travel speed to decode travel mode.

Accelerometer or equivalent

o To validate GPS data and track movement out of home where GPS signal is unavailable.

o The device should have a sampling rate that would enable it to detect falls as an adverse event (typically 5–8 Hz).

Data output requirements:

• The system should accurately track the following indicators:

o Type of travel mode (i.e. walking, vehicular).

o Time spent per travel mode (per day).

o Total distance travelled from home (per day).

o Total distance travelled per travel mode (per day).

o No. of walking tracks (per day) (walking track identified by speed ≤5 km/h) [18, 19].

o No. of steps (per day).

o Time spent out of home (per day).

o Time spent in location (per location per day).

o Location (latitude and longitude in SVY21 projection).

o No. of activity nodes (per day) (defined as places participants stayed for ≥5 min [9, 18].

• Spatial format in latitude, longitude and fixed projection.

• Retrieved location data should be exportable for geospatial mapping.

• Retrieved walking data should be exportable in commonly used data formats.

Older adult-customised design/feasibility requirements

• The tracker should operate without additional input from users.

• The tracker should be durable and resistant to adverse weather conditions.

• The tracker should be small, lightweight, and non-intrusive or distractive.

• The tracker should be safe to operate and socially acceptable to older adults.

Reliability requirements:

• The RFID reader should last continuously for at least 7 days.

• The system should require minimal training to operate.