The DA-066 unit is a standard part of the DA-605 Drive-Alert. When a vehicle is detected the DA-605 receives a signal and triggers the DA-066 to send a signal to activate DA-068 Plug-in Remote Chimes and/or DA-070 Battery-powered Portable Chimes. The DA-066 can also be used as a "test" or "call" button to manually trigger these chimes.
As an accessory, the DA-066 (in conjunction with the DA-068 and/or DA-070) can be used as an add-on to the DA-500 or DA-600 Drive-Alert models. Sometimes a customer who has one of these systems later decides he/she would rather have remote plug-in and/or battery-powered chimes as alerts instead of the piezo whistle that comes standard in the DA-500 and DA-600. Instead of buying a completely new system, adding these accessories to the existing DA-500 or DA-600 gives them these features, plus chime.