The 660-PB version is ordered most often because of the Momentary signal accepted by most power supplies.
Momentary signals are delivered as a short, single ''pulse-type'' signal. When power supplies receive the signal they know to go into action.
A typical application using 660-PB is to mount the unit under a desk so the person can ''buzz in'' someone through a door.
When the power supply receives the ''pulse'' signal from the push button, it knows to unlock the door.
The other version of this button is the 660-T4, which is a Toggle type signal. It delivers a constant signal when activated
and is similar to a light switch mounted on the wall. When activated, it delivers constant power.
Some power supplies can receive either type of signal, but others can receive only the Momentary signal type.
