Maybe you are thinking of UV filters? I was referring to lens filters like this - http://www.adorama.com/HY58RM72.html which only allow infrared rays above 720nm to pass through the glass.

Is this better/worse/ or just the same as using a infra-red lens filter for (D)SLR cameras?

A choice? Last time I looked around there was only 1 choice for cable in my town.

If he can get all the street signs and address numbers removed too then the terrorists won't be able to find anything