Aqara’s cord-free presence sensor runs for up to three years on battery power

The $50 sensor runs on two coin cell batteries so you don’t need a nearby power source for installation.
Business Wire

ams Launches Industry’s Smallest Proximity Sensor to Enable Integration of New Functionality in Space-constrained Wireless Earbuds

New TMD2636 fully integrated proximity sensor module for True Wireless Stereo (TWS) earbuds is supplied in an ultra-low-profile 0.35mm package and occupies a volume of just 0.7mm 3 The sensor draws on ...