SIM Card Spy Ear
Just take your SIM card out of your cellphone and stick it in this mysterious black box that's about the size of a bar of soap. Hide the $85 device in an inconspicuous location wherever you want to do your listening, and then when you call your cellphone number from another phone, you suddenly have ears in exactly the right places.From Surveillance: SIM Card Spy Ear for Nosy Neighbors and Private Eyes - Gizmodo
Cool. I have no need for this but I really want one. If it had a cam-phone mode I could use it to keep tabs on my cat.