Sounds similar to the heated cat house I use. They don't warm up until they cat sits on the pad. Those I do use. I bought one different kind where the pad stays warm constantly. The cats love that one the best but it makes me uneasy. Good to know there's a safer option for chickens for those who wish to provide extra heat.For years I've been drooling over the Sweeter Heaters, but they're so dang expensive. Last year, I finally got 3 of them, one for each coop that I normally use. They are safe, and are not power guzzlers. For the record, they do NOT heat the coop, but they do heat the birds. The way you test to see if their working, is to hold your arm under one for a minute. Your arm should warm up, but not the surrounding area. It's kind of nifty how it works. We've plugged them into a thermostat, like a thermal cube. When it drops below 50, they will turn on automatically, then turn off when the temps reach 52. I'm still waiting for it to get cold enough to actually test them out.
We put them in early. My birds don't LIKE it when we make major changes to their set up. I didn't want them to be afraid of the "boogie man heater", and stay on the other side of the coop. Now, they are used to them being in there, so it won't be a problem when it gets cold.