Our popular Unilab Light Gate is fully protected against incorrect connection of signal or power and supplies from 9 to 25V a.c or d.c. can be used. A signal LED indicates that the unit is functioning correctly when obstructed.The unit is compatible with all of our timing devices such as: Motion QED (B8H28020) Fast timer (B8H28573) Centi-Second Timer Module and Stopclock (B8H27749 and B8H27507) and Scaler-Timer (B8H28925).