You can buy a frequency scanner. Some are fairly cheap and others run up to around $150.00 It doesn't help though when you are in the air and someone flips on the radio but at times I think PCM fail safe settings are a good idea, especially if its a big airplane (jet, gasser, etc) - a lot of people set up the failsafe to go into a snap to lose momentum. Yep, the plane is toast but less likely to keep going out of sight and injure someone. Never used one of these so not sure if its worth the $50.00

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We fly at a public park and during the weekends there are soccer games, baseball/softball games and other functions going on so a plane with a lost signal could be disastrous if it got into a populated area.