2 supplied as standard equipment in product codes: MHA2000 & MHASYSTEM.
You can add as many PIR sensors as you wish. Simply set the same site code as the main system and set zone code with dip switches then select where you want to site the sensor.
The sensors can also be immune to most pets false triggering the alarm by the attachment of special blanking panels supplied. They can detect movement up to 18 metres away over a 120 degree arc and then transmit its signal back to the control panel up to 25~30 metres.