Radios can be dropped while in their active state, making them a highly effective lure.
Radios can be thought of as the more reliable version of egg timers in that the noise they produce will last until the monster finds and destroys the radio. The trade off is that egg timers do not emit noise immediately, giving the player far more time to find a safe place to hide. As such, it is advised not to use a radio when a monster is nearby, as even a quick "tap" of its active state generates noise that will attract them.
While in the player's inventory, an active radio will not make noise unless it is the currently selected item.
Although all three monsters will seek out an active radio, the Hunter's reaction is especially swift in that it will immediately emerge from a nearby vent in the same manner as if an alarm had been set off (assuming it wasn't already roaming the halls).
Radios can be found practically anywhere, but are more common in the lower levels of the ship, particularly the Engine Room.