I bought a SigmaSports PC-7 a couple months ago. Worked fine on the half-dozen occasions that I used it, but now it (the HR) only registers once in a great while. I've replaced the battery in the sensor with no success.
I bought this unit from Nashbar - are they going to exchange it for me without a hassle, or is there something else to try? (yes, I've wet the sensor, etc. -- didn't have a problem previously).
I had a Sigma PC14 and had the same problems that you are describing. Also purchased from Nashbar and I returned it about a month and a half after I got it for a full refund. I traded up to a Timex and I'm lovin' it.