These are handy little boards if you are interested in monitoring the level of a liquid in a vessel.  They use Darlington Transistors which enable this circuit to work with very clean (low conductivity) water.  Unlike other water level detectors that rely on a float switch, this does not require any moveable switch (although one can be used, if desired).  It detects the presence or absence of liquid at the tip of the probe.  The probe can be simply 2 wires that when they both come into contact with the liquid at the same time, a relay closes.  The 10A relay(s) on these boards can turn on or off a pump, solenoid, alarm (up to 10 A) or be connected to a digital input line on your DAC card for event logging.  They require 12VDC for operation.  This board is available in 2 versions:

	Version 1: $10.25 One Probe / One Relay.  Useful for detecting the presence of a spill or leak.
	Version 2: $19.00 Two Probes / Two Relays.  Useful for detecting high and low level conditions.