ALC-1 applies an adjustable voltage to your transceivers ALC input port to stop it from transmitting power into your amplifier.  It is triggered by the PowerMaster wattmeter SWR threshold relay.  Some amplifiers do not allow interruption of the PTT line and this is a good way to stop the RF from damaging the amp by shutting down the transceiver.

The Array Solutions ALC-1 Transmitter Inhibit controller interfaces between your amplifier’s ALC output, your PowerMaster PTT connections, and your transceiver’s ALC input to provide fast, rapid protection of your transceiver and amplifier when a sudden high VSWR event occurs.

The Array Solutions PowerMaster provides a PTT feature which can be used to unkey your amplifier when a VSWR reading above a user-selectable pre-set limit occurs. However, when this occurs, your transceiver’s output can be hot-switched since the amplifier is being unkeyed while your transceiver is still putting out full power. Further, some amplifiers are designed such that they do NOT unkey as long as RF is present to eliminate any possibility of amplifier hot-switching until the RF input has completely decayed to zero. So these amplifiers can be subjected to a momentary high VSWR resulting in possible damage.

ALC-1 Manual