I was fiddling around with my HR strap because I need to get fit, when I realised that the Samsung S7 (and earlier/later models i think) has ANT+ built in. Managed to pair the Garmin HR with Samsung Health app pretty easily after checking the strap still works with the Garmin Edge, and then managed to get it working with Strava App on the phone.
Just go to the Record screen on Strava, then Settings, then Sensors and it should find it if you've been wearing it.
Now I can record the HR when out for a run/cycle etc.
It's a really old Garmin strap too, think it came with a Garmin Edge 705.
Thought it might be useful for some people.
Have used my last 2 android phones with an old garmin ant+ hr strap. It's useful for when I'm in the gym or using trainer road on the turbo.