The HRM-Dual is Garmin's attempt to add Bluetooth support to a heart rate monitor and it is a pretty poor job.
It has no memory so the data needs to be captured immediately. That means it won't work in the pool but also means that if there is any loss in signal, you will get drop-outs. See the video below where I show my training data, including Zwift, where sections would be missing.
It is also tricky to replace the battery. There are four screws and they are inset. Garmin says use a Philips #0 screwdriver, but if you do that you will destroy the screws and find yourself with no way to get it out. Use a Philips #00 head, instead. Or just buy a different heart rate monitor.
The video below is not the only one I have made about it. Initially, it seemed a nice heart rate monitor. Then I made this second one about the dropouts, and later one complaining about the battery replacement process. It is, in my opinion, inferior in every way to the Polar H10.
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