Self-Winding Watches May Hold the Key to Forever Wearables, Animal Trackers

Kinetic energy is around all day, but solar energy is not.

In devices with low energy requirements, such as wearables or animal trackers, all the energy needed can be supplied by kinetic energy. For example, a watch can be powered by a tiny pendulum swinging inside it, generating enough power to move the tiny hands and overcome friction in the watch’s movement. Even a deskbound office worker can supply all the energy needed with an occasional flick of the wrist. No battery or winding is necessary.

The Rolex Perpetual, first introduced in 1931, was self-winding. A pendulum device supplied all its power. Could such a device be making a comeback? Image: Rolex.

The self-winding watch, patented in London in 1780, went on to power some of the finest Swiss watches, including the Rolex Perpetual in 1931. Despite this ingenious device, the watch came to rely on batteries with the onset of the quartz watch, which was more accurate and far cheaper than Swiss watches, self-winding or otherwise.

European bison with a GPS collar made by VECTRONIC Aerospace has a battery that can last 4 years. Image: Rewilding Europe.

Animal tracking is a whole other story but with a similar thread. Animal tracking devices also need to have perpetual power—which no battery can supply. Indeed, the battery in an animal tracker is the factor that limits its usefulness. An animal can only be tracked for as long as the battery has a charge. After that, the naturalist must find the animal (good luck with that now that it has no working tracker), sedate it and replace the battery in its tracking device. Not a fun time for either party. Wouldn’t both prefer sedation and trauma to occur only once?

For animal tracking, a pendulum device such as that used in self-winding watches, begs to be applied. A wild animal has kinetic energy in abundance and would not miss the little of it that is required to power a tracker.

Modern wearables, such as athletic wear studded with sensors, could be easily powered by the athlete’s movement. Why not have the flex in the sole of a runner’s shoe provide the power to an onboard microprocessor instead of a battery? Hysteresis generates energy normally wasted as heat. Chafing of clothes can be irritating, but one layer of clothing sliding over another can also provide useful energy. It’s a small change, but sometimes that is all that is needed.

In “Energy Harvesting for Wearable Technology Steps Up” (IEEE Spectrum, January 2024), we learn about researchers who are harnessing the energy available to wearables in lieu of batteries. More modern devices than the pendulum, namely, piezoelectric and triboelectric generators, can harness the energy in “bumps, jumps and strides to create tiny but still useful trickles of current,” writes Julianne Pepitone.

Caltech’s Wei Gao has developed an “electric skin” that reads heart rate, temperature and other biometrics that was first made of rubber. Sounds as if it would be too hot? It was hot by design. The lactate in the wearer’s sweat, combined with oxygen created pyruvate, is essentially a biofuel burnt in a mini fuel cell to charge capacitors in the e-skin from 1.5 to 3 volts for about 60 hours. The next iteration of e-skin replaced the rubber and fuel cells with sheets of Teflon and polyamide, which slid over each other to create static electricity. It wasn’t much (0.94 milliwatts) but it was enough. Gao’s next design uses solar power and 3D printing to make e-skin components that are small enough to be embedded into the e-skin.

The Kinefox wildlife tracker concept was developed by a research team from the University of Copenhagen’s Max Planck Institute. Image: ResearchGate.

Solar has been the power source most often sought in outdoor trackers and monitoring devices. However, solar power varies throughout the day and season. Solar power will be of little use in tracking nocturnal animals. And as IEEE Spectrum points out, it may be difficult to install a solar panel on a bison.

Researchers at the University of Copenhagen’s Max Planck Institute, inspired by the pendulum device first used in self-winding watches, created a tracking device with its modern-day equivalent, a micro-generator designed specifically for wearables called the Kinetron MSF32. This, combined with a lithium-ion capacitor, the institutes’ custom GPS-enabled tracker and a Sigfox low-power transmitter, was named the Kinefox.

It didn’t go well.

“The first collar we put on the bison got destroyed immediately,” said one of the researchers. “They’re 900-kilo animals.”

The team hopes to do better with wearables for humans, who are lighter and gentler than bison.

The Kinefox sells for €270—far less than the €3,500 to €4,000 price that is typical of commercially available trackers.

Research on using kinetic energy to power wearables could also benefit continuous monitoring devices in remote or inaccessible locations that make battery changing a challenge.