Garmin makes an ANT+ heart rate sensor with a model called
the "HRM2-SS".


↑That's the one.
The battery is a CR2032, which is a common type,
but the screw hole for replacing it

uses the Torx standard.
The size is extremely small, and it uses T5.
T5 is a size that typically isn't even included as the smallest size
in standard compact Torx hex key sets,
so it's somewhat difficult to find.


I have one because of situations like this in the past.
It actually came in handy today too.


Can't get the focus right.


Got it.


If you're having trouble with this, we can do the battery replacement at our shop.
Since we don't always have CR2032 in stock,
it would be best if you could bring one with you.


Perhaps due to complaints, the current model uses a small Phillips head screw instead.
If you're using an HRM2-SS, it might be a good idea to check
the screw hole shape before the battery dies and you're caught off guard.