Will a PIR sensor work through a double-glazed window?

[AL_n]

Anyone know if a PIR movement sensor will work through a double-glazed window?

Thanks

Al

[fred]

In article , AL_n writes

No, glass blocks the long wavelength IR that they operate on.

[John]

I was worried in case my alarm would trigger if someone was outside the patio door - but it doesn't - can't get the indicator to trigger no matter how much I dance around outside.

[Andrew Gabriel]

With dual tech ones (combined IR and Microwave), microwave part can see through glass, so you need to be careful in setting the microwave sensitivity if that's going to be an issue.

[fred]

In article , Andrew Gabriel writes

I thought they were designed to trigger only when both the IR and microwave elements trigger? Initially intended to reduce the risk of false triggering in variable IR environs.

[Dave Liquorice]

Me to. An example of variable IR being looking at a window and the sun popping out from behind a cloud.

[Andrew Gabriel]

That's a perfectly reasonable assumption, and one that I shared until I actually used them. However, many of them have a feature called anti-masking, where they detect that someone has sprayed paint to mask them, by detecting microwave movement without IR movement. Depending on the model, this either generates an alarm, or a tamper fault. You can get ones without this feature, but it's hard to tell as the datasheets often don't say.

[fred]

In article , Andrew Gabriel writes

That's useful to know thanks.