Why spend $8 for a fake when you can buy a real
wireless door/window alarm from Dollar Tree for $1 each. Many stores do stock them so you don't have to buy a box of 60... or just sell the excess at a flea market/yard sale for $1.25 each. These work and work well. Warning labels can either be printed off a home computer or store bought at many places like Home Depot, ACE, Lowes, etc.