the analogue ones worked in either a 27mhz or 41mhz range, if memory serves. There may have been others later, but i clearly remember the interference they caused in these frequencies with Soviet military transmitters. I could make so many jokes right now about babies saving us from a Soviet invasion (when there were still soviets...) but won't out of respect for common decency...

To paraphrase the comedian, Greg Proopes, "I thought Australia would be this great, cool progressive place but it's really just Arkansas with beaches" or something to that effect...