Used a flat head screwdriver and mangled the case along with tearing the o-ring on my cadence sensor, luckily it just sits on my dedicated trainer bike so no worries there.
Learned my lesson and used a quarter on my speed sensor (outdoor bike) which worked much better…still not perfect but it didn’t destroy it.
I guess the trick is try to use something that has the most surface area covered. Really needs to be less force holding these things together or stronger plastic though.