The voice scramble feature of a two-way radio provides the user with more private and secure conversations within a group. When using voice scrambling, a radio will encrypt the signal it is transmitting. The receiving radio will intercept the signal and will have to decrypt it to make any sense of the signals actual message.
Anyone with a regular radio on the same channel will only hear noise or garbled transmission instead of the actual message in the signal. If the user wishes to use this feature in a group, then, all the members in the group must have radios supporting voice scramble or they will just hear garbled voice.
But, it should be noted, that this feature does not ensure complete privacy. Anyone with the same brand and model of radio as yours will be able to intercept and decrypt the signal and hear the conversation clearly.