The Case of the Missing Calculators

I have 5 calculators for my classroom. These are NICE ones. They can graph, they can do fractions, and all the basic calculator functions. I have three brand-spankin' new ones and two oldies-but-goodies. Recently, two of my brand new calculators have gone missing. I know I didn't misplace them, and they aren't allowed outside my classroom. Hmmmm... Obviously some of my kids are taking them and losing them in the black holes also known as their backpacks. I have put note on my board for the last couple weeks asking for them back. I won't punish them, I just want them back. Guess what? They're not back yet. Bummer.