nRF52840 keychain that chirps when your phone is left behind
A coin-cell keychain that notices when your phone BLE advertisement disappears and beeps so you do not leave it behind.
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How It Could Work
nice!nano / nRF52840 with piezo and LED, Zephyr or nRF Connect SDK. Phone companion advertises a known BLE packet. When RSSI drops below threshold for N seconds, chirp. Optional reverse: keychain button rings the phone. Related to OpenHaystack but for leave-behind alerts.
Estimated Specs
DifficultyIntermediate
Cost$15–$40
BoardNordic nRF52
ChipNRF52840
Suggested Parts
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