UHF (ultra high frequency) walkies are suitable for usage both indoors and outdoors. The waves do not travel as far as VHF but they do a better job at penetrating obstacles between the transmissions. VHF (very high frequency) walkies are generally more suited for surroundings which has almost no obstructions and tends to operate best at 'near-the-ground' tranmissions. Thus, it is more suited for outdoor terrains.