By the way, you can use the green light from HRM sensor as a flashlight in bjs2
Was also thinking it could be used for some sort of communication when BLE does not work or is too complicated similar to IrDA or NFC - sending via blinking (led or even display) and receiving by the sensor. Display to HR sensor is unidirectional but two sensors pointing each other could be bidirectional.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
Was also thinking it could be used for some sort of communication when BLE does not work or is too complicated similar to IrDA or NFC - sending via blinking (led or even display) and receiving by the sensor. Display to HR sensor is unidirectional but two sensors pointing each other could be bidirectional.