Can I use my smartphone as a thermal camera?
Yes. There are two ways to use your smartphone as a thermal camera.
1. Own A Thermal Camera Handset
The first way, and also the best way is, to buy a thermal camera phone. This type of smartphone comes with integrated thermal camera and built-in APP, just tap the APP to make it work. Blackview offer this type of products with most affordable prices, meets the needs of those who have limited budget.

Related post, What phones have thermal camera?
Read also, here are the best cheap rugged phones list for checking out.
2. Buy The External Accessory
The second way is, to buy the external accessory which is compatible to your device (include Android and IOS). As you can see from the picture below, the gadget under the iPhone was a thermal imager. Usually, these type of accessories were supplied by FLIR company.

But, there are some disadvantages to use the gadget. Such as you need to take it with you when you want to use it, and you should be aware of protecting it dropping from the floor, etc. What's more, its price is almost close to a thermal phone's price.