Motion sensor trigger cameras

I was wondering if anyone could answer a question for me...I'm a total novice to video so I wonder if someone could help me...I was considering purchasing one of these motion sensor cameras that gets triggered when an object enters the video area...Someone told me that one of the problems with these cameras is that with the filming, when you go back and review what was on the tape, there is sometime a break in the taping which will exclude some of whatever is being filmed..Is this true????????

Usually when triggered they record for a set time, so if the action goes on longer than that, then you'd lose it.
It's a balancing act between running out of tape or memory card completely, and missing bits of the action.