I haven't purchased one anywhere yet. I'm just wondering for future projects. Here's an example.
We have a bunch of infrared "heat guns"(they sense temperature with infrared) laying around the house. As far as I know, the sensors inside aren't the fancy type you described. Theoretically, then, I would be able to take the infrared sensor out of the heat gun, find the i/o pins, and hook it up to my Arduino?
I suppose I would need to know what voltage corresponds to what temperature. Would I find that out through my own calibration?
That's one possibility - another might be that if the device has it's own readout display - then it likely has a microcontroller in it, and it might already supply a serial port you can read. That's a lot of "ifs" I know - but that's the essence of hacking and reverse-engineering.
For instance, Harbor Freight sells a cheapo digital caliper that inside - has a convenient output for serial data - which can be easily read by an Arduino. People use them all the time to add DRO (digital read-out) capability to their DIY CNC mills or other tools.
Those IR testers may have something similar - a lot of cheap tools do. Or they may not. Just google around - you are likely not the first person to want to hack something (especially if it is easily available on the marketplace - things get less likely when the item is "special" or otherwise difficult to obtain because of rarity, age, or other reasons) - so it is likely someone else has done the "hard work". Google "Arduino" and the name of the part and/or model number information (and/or in the case of Harbor Freight tools - add their name to the terms. For example, searching:
"Arduino Harbor Freight IR thermometer"
...turned up this:
...and I wasn't even trying hard.
:D :D :D
You generally aren't a special snowflake (except when you are - in that case, take the bull by the horns and start your hacking journey - sometimes, the best way forward on such a reverse-engineering adventure is to publish about it - sometimes, others will have the same issues and want to hack the device the same way).