Scosche Rhythm on-switch protector
This popular optical armband-heartrate monitor is very good in all respects, it is just a bit too enthusiastic. The on/off switch is beneath the rubber surface, and it doesn’t take much pressure to activate it. All good when you actually want to switch it on, but not when it is in a gym bag or in a pocket.
One bump and it’s switched on, and there goes the battery charge. It’s possible to design and 3D-print a custom brace to protect the switch, but what if you only have a credit-card (any credit-card-sized plastic will do) and a pair of scissors?
Cut off a strip of the card, bend it, and put it through the strap holders.
The card strip fits snugly, it won’t fall out, and you can leave the protector on while it is on the charger.
Don’t use the part of the card that holds a chip, that doesn’t bend well.
NB: it is advisable to use an expired card.