I took my Polar RS800CX into a local jeweler / authorized Polar repair; and he had a very difficult time getting the wristwatch unit plastic back removed without tearing it up.
The dime slot took a beating, Polar had it torqued down too tight.
Next time (very soon) it will have to go back to Polar. The jeweler said he wouldn't be able to work on it again.

The HRM was marketed as "multi-sport" so imagine my surprise when it did not transmit while swimming.
So I will be using my swimming HRM on the bike while the RS800CX is getting serviced.
It won't show my cadence in the polarpersonaltrainer.com website but it handles the important stuff - speed, distance, heartrate.

My employer gives us financial incentives to log our physical activity using the VirginHealthMiles site; it only accepts the web-uploadable Polar HRM's and the GoZone pedometers.
So I am pretty much locked into Polar for now.