We write a lot about power here at Health Tech Insider, because the digital electronics used by wearable Health Tech devices require power. Consuming less power — or storing more energy — means that a device can run a lot longer between charges, or be smaller, or both. Which makes the devices more attractive and convenient to use. Of course, the ideal would be a device that doesn’t consume any power at all when it’s not busy doing something. We have written about such a device that switches on using the power from a sensor’s signal. Here we have another zero-power solution: one that is triggered by the very thing that it is designed to detect.

Researchers at Northeastern University developed the device in response to DARPA’s “Near Zero Power RF and Sensor Operation (N-ZERO)” program. The team built an infrared emissions detector that remains dormant until it is exposed to infrared light. The clever design relies on a Rube Goldberg mix of electrical and mechanical components. It starts with a matrix of sensing elements, each of which is tuned to detect a specific infrared wavelength. When struck by the right light, the temperature for that tiny element spikes as it absorbs the energy from the emissions. This heat causes certain portions of the device to expand, which in turn moves contacts that close a circuit and wake up the device. The result is a device that lie dormant — consuming no power — until there is something to sense. And the fact that it uses a matrix of detectors tuned to different wavelengths means that it can provide a spectral analysis of the infrared emissions, which in turn can provide information about their source.

The DARPA program is intended to create devices for national security programs, but this technology could have other applications as well. Biometric sensors that could be triggered by a specific input, such as a chemical or light wave, could last indefinitely on standby. This would be convenient in terms of extended shelf life, as well as long-term use without needing batteries or recharging.