The deck is fairly immune to inspection -- and it doesn't tend to trigger from being handled, only from a toss in the air or a drop. Try throwing and catching it, dropping it from one hand to another, or letting it go a short distance above a table or other surface.

A gambler's poker cards are just one example of how to theme this effect. If you like, you can use the gag inside any kind of object you like -- a sealed wooden box, inside a stuffed animal, hidden in the heel of a boot -- you can get creative with it!