A major problem with earbud and smartwatch technology is Bluetooth itself, which requires a device that can receive notifications to be “always on”, powered up, listening for signals, exchanging handshakes. It would be much more sensible to use passive RFID-style technology for devices that receive notifications.
In such a system, the earbud or smartwatch would normally stay unpowered (except for the clock in the watch), and the phone would ask the earbud or watch to wake up with a radio pulse that includes an ID code. This radio pulse would be stronger than a normal Bluetooth signal, strong enough that the energy in the radio wave itself would be enough to activate a tiny circuit that wakes up the processor in the earbud or watch. So when you’re not using it, it uses zero power, so “casual” users need not recharge every device every day.
My smartwatch has a nice feature: it vibrates me when it can no longer communicate with the phone. An earbud could have the same feature, playing an out-of-range sound. This feature, too, doesn’t need an always-on Bluetooth exchange; the phone could send a “radio blip” every 10 seconds that, instead of waking the earbud or phone up, would just prevent it from waking up.
The nice thing about this approach is that the technology is proven; it already exists in the form of RFID tags (tags that contain no battery, which can be used to identify objects such as parcels or passports or items in Wal-Mart).
Unfortunately, the most recent version of Bluetooth (4.0 aka “Bluetooth Smart”) doesn’t include a zero-power mode. Fortunately though, it does have a low-power mode, which dramatically increases the battery life of not just accessories like watches but also the life of your paired smartphone. It is claimed that devices with “coin batteries” can now run for months on Bluetooth 4 “with the same range” as previous versions of Bluetooth, although my Googling has so far found me no explanation of just how the new standard saves energy.
Perhaps Bluetooth Low Energy is enough. When combined with tiny thermoelectric generators, someday we’ll enjoy wearable devices that never need to be recharged. And perhaps separately, our phones will gain the ability to locate RFID tags. So I can finally find my keys.
