Know What I Need, Don't Know What To Call It.

Maybe one of these to do it properly

or if it's a hobby?

Either way search for a temperature controller - I got 7million hits. Most have alarm points you can use.

So you will know if there is potential for a fire or frozen pipes but you won't know for sure. Sounds like a stress inducing data point. More data needed!

Most any cheap PID loop temperature controller with relay outputs can be setup to do what you want by using the main output and an alarm output to activate at the selected upper and lower limits you want.

They are around $20 on eBay and I use the all the time so I know they are reliable.

A PID loop temperature controller. Now we're talkin.

Any specific model come to mind? I need something basic and simple to program that can have a single relay open if temperature goes say, below 50 or above 90. That's it, that's all I need it to do. And 110v supply.

Perfect! I have one on the way.

My goal here is to keep the setup clean and very simple. So I will connect this controller to a new device called an XProxy which will send me a text if a location's temperature goes below or above a set point.

An interesting thing about the XProxy cellular device is it only has 2 wires and requires no power, no wifi, no cellular contract or sim card. It just works. It can be connected to anything with a NC dry contact. Pretty cool.

Thanks for everyone's help.

What a deal. I was going to suggest the Red Lion unit, because for OEM applications in pharmaceutical, they are low price and meet specs, but for this type application, with no picky pharmaceutical engineers involved, that price blows the Red Lion out of the water.

How is the programming for band use on those models? I would have had to help the OP program a Red Lion. Got to be the toughest set of directions ever to follow.

The instructions can be found online and are not too hard to follow all though I think they could be better by giving a more indepth coverage of the additional functions and setting that the units are capable of.

So far the only problems with setting them up by the instructions is with the cheap chinese knockoffs of the RKC REX-C100 units.

Some of them have a limited amount of functional settings to work with. Either the setting as a whole is unable to be accessed or if changed it doesn't do anything like changing the display from C to F or setting a certain type alarm function.

The program value can be changed from the factory default but the actual unit doesn't respond to the change.

Yes there are 24 volt DC versions too.

Temperature controller Omron, Cal, Watlow are some that come to mind. There are many others. Most have auxiliary contacts that can be programed as an alarm output. And set to min or max temperature. You will need to check the operation of this closely if you need specific set points on the device. As some are just plus or minus variance.

I can design a simple system for you for $50

I'm all in if you are serious. I'm not having much luck getting this to work like I need. This should be easy.

greenhouse temperature range monitor alarm

http://www.absoluteautomation.com/applications/greenhouse/index.html

I recommend that you go with no.9, whom I just gave a GA to. I don't know what your temperature normal fluctuations might look like, but no.9 is correct in comments regarding type' k' thermocouple vs PT100 sensors.