Garmin watch as a power meter

Question

I've a Garmin fenix 6 watch and was wondering can I use my watch as power meter if I connect my watch garmin bike sensors ?

Answer 1

There may be some confusion with terminology here. A power meter measures power, usually by measuring the strain in some drivetrain component (i.e. how much it flexes when pedaling). You need to physically attach strain gauges to the component. This is usually a crankarm or pedal spindle, but strain gauges have also been mounted to bottom bracket spindles or inside rear hubs.

The Fenix 6 is a watch, and it's nowhere near the drivetrain, so it can't be a power meter. It can track heart rate by itself, and heart rate can also be used to pace a workout. (see footnote) In that sense, it's like any other cycling computer, except that it's also a watch.

Power meters usually broadcast their data over two protocols, ANT+ and Bluetooth (older meters may only use ANT+). In any case, the Fenix 6 appears to have ANT+ compatibility, as do a few other sport-specific smart watches. Generic smart watches like the Apple Watch most likely lack ANT+, but they could accept Bluetooth connections. Their software might not take power meter data, although some of the latest ones can. The ANT+ page for the Fenix 6 Solar, European model lists many compatible power meters, including power pedals by Garmin and Favero, crank-based power meters from Quarq, Shimano, Rotor, and Easton, and, as an aside, One Giant Leap's Kayak Power Meter (to emphasize, this is for kayaks, as in the ones you use on water).

Occasionally with technology, the devil is in the details. One Reddit post claimed that their Fenix failed to display the cycling dynamics (an advanced metric) from their Favero power meter pedals. There may be other relatively minor issues like this with other manufacturers. It could be that the Fenix lacks some implementation of one of the features on some power meters, but the core features (it will need both torque and cadence) would likely be present.

Again, the Fenix 6 is impressive, but it can't measure or estimate cycling power by itself. The OP asked if the watch could be used as a power meter if they connected it to unspecified Garmin bike sensors. If you want to use your Fenix 6 as a cycling head unit, you would want to get a bike mount. If you are primarily a cyclist, I would normally recommend just getting a cycling-specific head unit, which will have a larger screen and cost less (perhaps a lot less) than the Fenix 6. However, the OP already has a Fenix 6 watch, and it would obviously be fine to reuse it as a head unit.

Footnote: other ways to measure power

It's possible to estimate power from air resistance, e.g. the Notio Konnect or the Power Pod, i.e. you are not directly measuring power, but you're estimating it from some assumptions. This requires a device with a pitot tube at the front of the bike. This type of device has mostly wound up being used to measure aerodynamic drag when paired with an actual power meter. It's also possible to estimate power from chain tension. No active power meters do this, but Polar once made such a unit.

Running power is starting to become a thing. There is some detail here. In brief, some modern sports watches and general smartwatches can use the accelerometers and altitude sensors to estimate the work done to move the runner vertically (against gravity) and horizontally (i.e. forward). Again, some assumptions need to be made, and the watches only have GPS to measure speed, which has some accuracy issues. The Fenix 6 appears to need unspecified other sensors to measure running power (e.g. perhaps a footpod containing accelerometers like Stryd). More modern sports or smartwatches can do it natively.