Technology Review reports that an attacker my be able to pick up encryption keys from cellphones with a TV antenna:

The antenna was detecting radio signals “leaking” from the transistors on the chip inside the phone performing the encryption calculations. Transistors leak those signals when they are active, so the pattern of signals from a chip provides an eavesdropper a representation of the work the chip is doing. When Kenworthy tuned his equipment to look in the right place, a clear, regular pattern of peaks and troughs appeared on his computer screen. They could be seen to come in two varieties, large and small, directly corresponding to the string of digital 1s and 0s that make up the encryption key.