Hi, I have an Angelcare monitor, have been very happy with it, still using it even though DS is 2 next month
False alarms have happened when he's rolled away from the mat (especially as he's got bigger and curls up in a ball in the corner of the cot ) but that has also been a kind of reassurance that it's working IYSWIM.
Much better (IMO) and more modern are very small monitors that clip onto baby nappy - used respisense- fab for daughter (not great for boys if wee wee get in it - which happened with ours) and snuza for boys (waterproof). Can be on baby all day including when in pram etc Any questions please ask. I bought both mine from Ana wiz (on line)