Anandghan Waghmare
Publications

WatchLink

UIST 2024Low-cost sensor add-ons for smartwatches through the watch's ECG interface.

WatchLink is a low-power communication method that lets smartwatches use their existing electrocardiogram (ECG) hardware as a data interface. It allows inexpensive, low-power "add-on" sensors to connect to the watch and extend its capabilities for specialized needs, at a fraction of the cost and power of protocols such as Bluetooth Low Energy.

We characterize the ECG interface as a communication channel on commercial smartwatches, design a simple transmission scheme using commodity components, and build a suite of add-on sensors, including UV light, body temperature, buttons and breath alcohol, all meeting their testing objectives at low material cost and power.

This opens the way to personalized, user-centric wearables with a cost-effective path to new functionality.

Smartwatches that take an ECG already have metal contacts (yellow) on the back and crown. WatchLink reuses them as a data port.
Smartwatches that take an ECG already have metal contacts (yellow) on the back and crown. WatchLink reuses them as a data port.
The idea: an add-on sensor sends its readings as a tiny electrical signal through those contacts, and the watch records it just like an ECG.
The idea: an add-on sensor sends its readings as a tiny electrical signal through those contacts, and the watch records it just like an ECG.
A UV-light sensor built into a 3D-printed watch case. It stays in contact with the crown, so it can stream readings continuously.
A UV-light sensor built into a 3D-printed watch case. It stays in contact with the crown, so it can stream readings continuously.
A body-temperature sensor on a thin, flexible circuit board (front and back).
A body-temperature sensor on a thin, flexible circuit board (front and back).
The temperature sensor stuck to the inside of an Apple Watch strap.
The temperature sensor stuck to the inside of an Apple Watch strap.
A breath-alcohol sensor on a wristband worn next to the watch.
A breath-alcohol sensor on a wristband worn next to the watch.
An extra physical button for the Google Pixel Watch, connected through the same ECG contacts.
An extra physical button for the Google Pixel Watch, connected through the same ECG contacts.