NWR Fitness monitor gadgets/heart monitors and running

I used a chest strap - Polar (H7 I think) with a fairly basic Polar watch for a while and am looking at a watch upgrade, likely to one which has wrist-based HRM for better monitoring when I don't wear a strap (most of the time).

Does anyone who has a chest strap know if I can use either wrist or chest measurements and how it's done?
Does the watch automatically recognise if a chest strap's operating and use the better input instead or is it some more manual thing?
And has anyone experience of a Polar strap talking to other manufacturers' watches?

About to embark on some serious research but the above would save me some time :)