My Oregon Scientific JTR168LR works great.

Every solid object the signal has to pass through reduces its strength and distance it will reach...greenhouse covering, window, house walls. My greenhouse is around 75' from my house and even from the greenhouse to the nearest window, the 100' wireless unit I had was very hit and miss. I use the unit in the link below and have had no trouble with it in the year and a half I've had it. It has saved my plants several times!!

But...wireless alarms (I assume that is what you are most concerned about) in general are not foolproof. We're going to have a phone line run to the greenhouse this spring so we can switch to a hardwired alarm in the future.

Here is a link that might be useful: Wireless Data Logger

Josh,

I wasn't aware that there were alarms that used phone lines. Does it have to have service or just the phone wire? I have a wireless which sometimes acts up and doesn't give me a remote reading. It will suddenly just pop back in without my doing anything. Batteries have been changed so it's not that they're dying. I'd like something more dependable since so much hinges on it.

MollyD

thanks both of you for your feedback. I went back to Lowes and got the next model of thermometer up from the one I had and it works really well. Happily, they charged me $19.99 instead of $29.99. I said nothing seeing as it was the second one I'd bought from them !

Simon

See the following link, Molly. There may be other brands, I'm not sure.

Here is a link that might be useful: Sensaphone Alarm

Thanks Josh,
MollyD