The Wallbotz 310, 400C, and 400, and Rackbotz 303, 310, and 400 products from Netbotz (now APC Netbotz) are all discontinued wall-mounted or rack-mounted datacenter environment monitoring products. They all have one common feature, an external sensor port with a wide variety of possible inputs. New old stock sensors still command a high price on ebay, but the most useful sensors (dry contact and temperature) are very easy to implement.
The external sensor ports on the Netbotz devices use the same physical connector as a PS/2 mouse or keyboard. An analog voltage is sensed on the input pin and useful data is derived from that.
For dry-contact inputs, simply connect VCC through a 1K-10Kohm resistor (the value is not critical) to INPUT through the relay contacts, so that INPUT will be pulled high when the relay contacts are closed but otherwise will float low to zero volts (there is an internal 100Kohm pulldown resistor inside the Netbotz). Then, the Netbotz advanced view software can be used to set up a dry-contact input.
For temperature sensors, the voltages output by the official TS100 sensor from Netbotz on the INPUT pin indicate that it almost certainly contains an inexpensive TMP36 analog voltage temperature sensor IC. Simply connect a TMP36 sensor's +Vs, GND, and Vout pins to VCC, GND and INPUT respectively and set the input type to a temperature sensor.