Pat I was a security engineer for 15 years and that is a load of goolies,
Have a look on the window or frame, if you see a small white box then the chances are it is alarmed, and may be Sensitive, but it would have to be a really old alarm for this type of protection a window that needs protection in a domestic property is covered by an infra-red detector(PIR).
I had a customer who used to say the same to me, until I pointed out to them, that I felt untrusted, when they asked why I told them I was a security engineer and from that day on I never had to wait for them.
I think its a case of the customer wants to be there when your about.