The Delkim Plus Bite Alarm are the best I have ever used, they are extremely versatile, sensetive and reliable. They do not use the conventional roller wheel that most alarms use but instead they use a vibration sensor that does not use any moving parts. They also have very low batery drain and run on one 9v smoke alarm battery. Their only problem is becaue they pick up any vibration they sometimes beep because a rain drop has hit the line.