There are two basic types:

1) Ones powered off of the 120V lines and that have SAME.
2) Battery-powered models.

The SAME allows you have the unit in "standby" mode, but it turns on in the event of an emergency. What happens is that the radio is on, but the speaker is muted. When a special code is received, the unit "wakes up."

To me, SAME is only useful in a radio that plugs into the wall. Because the receiver is always running, running SAME on a unit powered by batteries does not seem like a good idea.