The Watchport/P looks a little different than the other sensors, because it has an attached infrared transmitter and receiver combo. It can detect distance as well as proximity. For example, you could use this as a "tripwire" across a doorway by mounting it on the door frame. An alert signal would be sent whenever someone walks through the door.
Water Sensor - Watchport/W
Water in a server room, or even in the wrong place in your house, is a bad thing. The Watchport/W detects water with two metal probes that protrude out about ½ inch from the bottom. When water hits the probes, the sensor detects the conductivity change and sends an alert to the monitoring computer.
Since the sensor only detects the presence of water and not its depth or weight, it may be a good idea for some applications to place multiple water sensors at different heights.