Home Depot Motion Sensor, On when power is turned on.

[hermanto@xxxxxxxxx]

Hi,
Trying to build a low tech alarm.
Bought a Home Depot Motion Sensor 180 degree Heath / Zenith for
floodlight.
Open the case, modify the connection  of the internal 24 V DC relay.
Now, it is normally open and the contacts are not connected to any of
120v line. Stable, as long as 120V power remains on. Good for driving
12 V siren (will add relay if necessary).

PROBLEM: Powering up always energizes the relay for about 1 minute
(warming up??). So after power blackout, will get false alarm, the
siren will go off for 1 minute.

Any solution would be appreciated.

Thx u