1.   Bluetooth, in contrast, operates on a radio frequency, so its signals can penetrate walls and briefcases.

2.   ELF signals penetrate not only water but also the depths of the earth.

3.   The higher frequency bypasses most interference and lets the signal penetrate walls better than the current generation of cordless phones.

4.   Their range is also better than older models, and their signals penetrate obstructions better.

5.   While the signal will easily penetrate sheet rock and wood, it can be completely or partially blocked by large amounts of metal.