I can't see why (or even how) a wrist-strap monitor should be less accurate than one on your chest. After all, it's only taking your pulse and the traditional way for a doctor or nurse to take your pulse is to feel for it in your wrist.
I use a wrist-strap blood pressure monitor every day, which also records my pulse (as I'm sure that they all do), and, while wrist measurements of blood pressure might not be quite as accurate as upper arm measurements, I've no doubt at all that it's 100% accurate as far as the heart rate recording is concerned.