How sensitive are pir sensors?

I have a lot of lizards in my house and am wondering if they'd turn the pir sensor on. I also want to know if small insects would turn the pir to high.

I think it is not going to work.
Are lizards cold blooded ?

A PIR sensor detects something big and something warmer than the background that is moving in front of the fresnel lense.

Perhaps a number of ultrasonic distance sensors. But I don't know how those sensors will respond to rain.

Erdin:
I think it is not going to work.
Are lizards cold blooded ?
Lizard - Wikipedia

A PIR sensor detects something big and something warmer than the background that is moving in front of the fresnel lense.

Perhaps a number of ultrasonic distance sensors. But I don't know how those sensors will respond to rain.

Thanks for the reply. I am glad to know. I actually don't want the lizards to activate it.

I kind of misunderstood your question XD.

Some good quality PIR sensor detect a moving human body at 15 meters or more.
Suppose a lizard has warmed under a lamp, and starts moving in front of a PIR sensor. If it is nearby a PIR sensor, say 2 meters and decided to move a little faster, it might turn on the sensor/alarm.

Or if the PIR sensor is looking at something hot, like a lamp or a floor heated by the sun. If something colder passes by between the hot object and the PIR sensor, the sensor also detects a change.

A spider right over the PIR sensor could also turn it on.

Conclusion:
Can PIR sensor be used to detect lizards: No, almost not.
Can a lizard turn on your alarm (with PIR sensors): Yes, it might happen now and then.