The ASCO series 881 compact signaling unit is designed to be used with the ASCO series 290 (2/2 NC) and 390 (3/2) valves. It has a compact design that allows it to fit easily into confined spaces. The unit electrically and visually indicates the open or closed status of the valve and does not require any special tools for installation. It comes with a standard detector support that is compatible with both reed switch and magneto-resistive (MR) UNI-type detectors.