Hmm... my watch doubles as a heart monitor, it has 3 sensors, one on the underside, then one on the top and bottom on the face of the watch. You put your thumb and forefinger on those top 2 sensors, and it reads your heart rate. It's pretty darn accurate too. But it's not constant, unless you wanna keep your fingers there all day.
As far as Body Bugg is concerned though, it doesn't do heart rate, it tells how many calories are burned based off movement, which makes it less accurate. And it's pretty expensive. But it can do about anything else, or so I hear.
I dunno, I find that the chest strap that came with my sports watch doesn't really bother me as long as I don't wear it too tightly. But to each his own. ;P