What I've heard is that they use a so called space blanket to stop alarm "eyes" from picking up the movement.
@Slaaiblaar you should be able to tell?
Not all passives are equal....this is what jou must remember. You get what you pay for. Passive come in all different shapes and focal patterns. Some 90° some 180°. Beams are a point to point laser/led light transmitted from transmitter to receiver.
Passives can be bypassed by crawling or moving very slow. Beams can be bypassed by avoiding the invisible lines, like in movies.
Garage door and gate switches can not be bypassed...if wired correctly.
A mix of all above is the best way to go.
Emergency blanket is BS.
Every person with alarm should test it atleast once a week. Then a gate motor is not a lock, it open and closes gates. Wire your IR beam at gate to your alarm. Using normally open point. If wire is cut or power is lost it will sound an alarm.