Wireless Motion Sensor slow to start

["KSG" <kangsu@xxxxxxxxx>]

I have a wireless motion sensor and I have tried setting on my alarm
and then starting in the back of the room to see how far I can get.  I
notice that if I do this test immediately after the alarm system delay
is finished the motion sensor doesn't go off, even if I jump in front
of the sensor.  But if I wait a few minutes, then it does catch me.

Is there some additional delay before the motion sensor starts?  Is
this to preserve battery life that it only checks to see if the alarm
is set every five minutes or something?

Thanks!

KSG