Chameleons are incredibly resistant to Hypothermia- its Hyperthermia that is usually the killer. They have all sorts of defenses against the cold, and there are chameleon species that endure nightly frosts (drops below 32F) during some seasons.
Personally I think, unless your house is commonly going below 0C (32F) in the winter I wouldnt bother, and even if it was, I have a feeling you would know about it and wake up- which would give you a chance to solve the problem.
They make a probe for food that does this. It is no more than a beeping. It has duel purposes as a bio-therm for quick temperature measurements. It can only be set at one temperature not a range like I think you guys are talking about. I could find out a price and the company who makes them if you guys would like. I do not really see the purpose of it. I have to agree with Will on this one as all chameleon species can endure so very low temperatures. If the room itself is getting to hot it would not be the basking light but a lack of air flow that is doing this and the animal should be moved into a better location.
this temp alarm is 19.99 and i dont think 40 f for more then 2-3 hrs would be a healthy thing for veileds. i was told by the breeder i got them from that i they are safe to 55 f any more and your looking at possible death .
If you get on a travel web site and look at the average temperatures I think you would be suprised. Two months out of the year it is 30 degrees or colder at night and only in the 60's during the day. I do suspect that alot of chameleons die at this time but it would probably be the lack of food not the temperatures. Veileds live largely off of locust, grasshoppers, and crickets that eat off of the nearby crops and seasonal things that grow in the region. These insects migrate when it is colder. I think this is why veileds eat things like birds and small mamamals. It also explains why they are so aggressive towards intruders into their terrioty. Only the strong survive these conditions. That is why people consider them so hardy.
your talking about wild chameleons not captive ones, wild ones are use to the harsher climate they know when it starts getting cooler so they warm up extra during the day to compensate for a possible cold night .A chameleon thats used to a cozy 70f nights and then all the sudden the night temp drops to 50f its gonna effect them i would think. now if the temp drops gradually over some time they aclimate therselves to that. and this temp alarm i have is not for food its a extech temp alarm and you gotta set it for it to be of any use if you just run the sensor to the room and set the time and procrastinate on setting the alarm its useless.
I guess over the years people have given so many recommendations that it is a "fact" as to how veileds are to be held in captivity. They can be found in three distinct climates in there natural enviroment.
1. Humid low coastal plains. 80's for the low day time temperature up to 110 for the high day time temperatures depending on the months of the year. 60-70 are usual night time lows. Humidity in these areas average 50% year round. 0-4" of percipitation a annually.
2. Southwest mountains in Yemen. These would resemble more of a "montane" species recommendations then normal veileds. Highs in the days from 60's to 80's depending on time of year. The night time temperatures range from 30-60. Recieving 80" of rain annually.
3. High plateaus. The temperatures are near identical to the southwest mountains. The main differences is the rain fall is 20" annually.
My research point to 2 having the biggest populations of veileds. That is hard to see with the recommendations. I doubt that a couple of years of captivity would genetically alter millions of years of evolution. They can survive these low temperature. If you are uncomfortable with exposing them to it then do not do it. I honestly keep my female in 2 despite recommendations. She burnt her casque when she was four months old. I move her in this catagory starting off so she could heal without the threat of aggravating it further. I just left her like that. It has been almost a year. No health problems since the casque burn which healed by itself. She was a little dehydrated after her first clutch. I honestly was overfeeding and I think that played a role in it. Any recommendation I have given about veileds is for 1. I do keep my male in 1 as the colors seem to be more dramatic. It is your pet for your enjoyment. You have provided them with the basics they need to survive specifics are up to you.