I have an angelcare monitor too. We are borrowing it from friends who didn't end up using it.
I haven't used the pads under the mattress because I have heard that they go off for no reason and I didn't want to become too much of a worry-wart (no offense to those that do use them - it's just that I would obsess because I can be a bit like that at times).
I think there's been another thread about this but a few of us with Angelcare monitors have found them to get a bit of interference if they are plugged in with other appliances or in certain areas of a room. It doesn't bother me too much because we play music in Gabby's room so it drowns out the interference most times.
If I was going to buy a monitor, I think I would just get a relatively inexpensive one that was just sound and none of the other fancy stuff. That's all I have used it for n e way!
I don't use it at night because Gabby's room is right next to ours and I can hear her as clear as day when she wakes up n e way.