PIR problem


I use a PIR on a GSM shield but it gets enabled without motion.
I put the sensor in a hidden place but still gets enabled. For example last time I got 5 messages:

  1. when plugged in (12:00),
  2. 1 hour later (13:03),
  3. half hour later (13:27)
  4. 15’ later (13:43),
  5. 1 hour later (14:43).

The sensor was looking on the wall of the room and was almost hidden.
I can’t understand what could be the problem. Could the sensor be faulty?

I use Arduino UNO, GSM SIM 900, PIR sensor.
The Arduino is plugged with a 9V adapter for the Shield needs.

I changed PIR% with a new one and now OK.

I have a similar problem with my new PIR sensors. There is now Feedback from the sensor (high / low). Can a check sensors on a table with a 100 watt roof light or is that light and heat source to strong to let the sensor calibrate and run. i use the Schema from the funduino sketch number 8