Does anyone have a trick to opening the wahoo rpm cadence sensor case. I have tried coins, fat screw drivers, break disc ( The sram disc almost matches the curve of the plastic case)
I have just about destroyed the plastic shell and have only change the battery 3 times!
jeff
I just dealt with this the other day, huge pain.
Might sound stupid but I had it around and it worked. The steel chain checker from park tool
I used a butter knife last week.
Mega annoying.
Oh good, not just me then.
I suspect something like this designed for taking apart phones/tablets would do the trick, but I’m too impatient to buy tools for a specific job and end up just hammering away at it with random things from my toolbox until it’s open.
Amazing that it’s still waterproof really.
I usually use a quarter.
I have a hard time getting mine to close back up completely. Not a great mechanical design.
I use a quarter or a loonie
Mine is full of nicks and marks from my attempts at getting it open. Used a screwdriver and a coin today and found that the rubber seal is split 
- possibly from using the screwdriver
Mine was mangled so much, I used vice grips to gently hold the bottom half. Squeezed it and voila. Mine is so mangled , this will be the only way to keep it alive. I have only changed the battery now twice and I feel I’m generally good with tools. grrr…
I sometimes use the back end of a fork or spoon, I have a few that fit the profile well
I also have found certain specific coins or tokens work well. I have a token from some game place that fits perfectly and it’s my go to and lives on my desk just for battery swaps 
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.
Similar. I just broke the shell and the gasket came out. I put it back together and it’s working but I bet not for long.
I got rid of mine and replaced it with a Garmin, which has an actual battery cover. On the Wahoo, I also had issues with the battery making contact and had to put padding behind it. Poor design all around.