Feature Request: Use RF power harvesting tech to keep AirTags charged by Wi-Fi

There was a time when tech news was full of talk about long-range wireless charging using a technique known as RF power harvesting – using radio waves to charge devices around the home, without the need for charging pads.

While companies like Energous and Powercast made big promises for the tech, what’s currently possible in the real world is far more modest. But Samsung has demonstrated that trickle-charging a TV remote by Wi-Fi is possible today, and the very compact nature of the tech means that it could similarly be used to keep AirTags charged …

The problem with long-distance wireless charging

We’ve discussed before the huge gulf between the vision of a box on the wall keeping our MacBooks charged, and the present-day reality of tiny amounts of power suitable only for trickle-charging devices with very low power requirements.

Under what are known as Part 15 regulations, the Federal Communications Commission (FCC) limits the maximum power output of an RF power transmitter to just one watt […] And since nothing is ever 100% efficient, the maximum power that can be harnessed is even less – even right next to the transmitter, that might realistically be half a watt.

But we can’t talk power without returning to distance. More specifically, the relationship between power and distance. Radio waves (and RF power is just a specific form of the same) are subject to the inverse-square law. This states that intensity is inversely proportional to the square of the distance from a source.

Get 0.5W one inch from the transmitter, and you’ll be down to a 0.125W two inches away from it (two times the distance = quarter of the power). At four inches, you’ll be down to 0.03W.

It doesn’t take much math to see that visions of powering a MacBook across the room from the transmitter any time soon are just pure fantasy. 

But RF power harvesting would be practical for AirTags

Realistically, we’re unlikely to see RF power harvesting used in an iPhone, let alone a MacBook. But it is a practical proposition for much smaller devices.

The tech required to receive power is extremely small – essentially an antenna no bigger than the Bluetooth one already present in an AirTag, incorporated into an equally tiny chip. While the power delivered from Wi-Fi is very low, so too is the power drain of an AirTag. When you think that a button battery can keep it powered for a year, then it’s clear that the power drain is tiny.

Consider, too, that AirTags spend a great deal of their time at home – at least overnight, and most of the time when it comes to things we don’t carry with us every day. The idea of trickle-charging AirTags via Wi-Fi looks like an eminently realistic prospect.

Wi-Fi charging would make AirTags true fit-and-forget devices

It might be necessary to make AirTags marginally larger to accommodate Wi-Fi charging, but to my mind, that’s a price worth paying. The whole point of an AirTag is that it’s a “fit and forget” device. We throw one into a bag, and then that bag can be tracked when necessary.

The problem with devices that need to be charged – or have their batteries replaced – very infrequently is that it’s extremely easy to forget. We’ve probably all done it with things that can go weeks or months between charges, like headphones and Bluetooth keyboards. There’s a very high risk that the first time we realize that an AirTag is out of power is the very time we’ve lost something and need to track it.

Keeping them topped up with power any time they’re within Wi-Fi range would solve that problem.

Given the possibility that they’d need to be marginally larger and more expensive, I’d be fine with an AirTag+ with Wi-Fi charging. But given that both size and price premiums would be exceedingly marginal, that might not even be necessary.

I’d love to see this – how about you? Please take our poll, and share your thoughts in the comments.

Photo: Nikita Ognev/Unsplash