The largest thermal camera I looked at was the Flir One Gen 3, which is 2.6 inches wide and 1.3 inches tall and has a built-in battery and two cameras. It's the most complex camera I've seen. This large camera body has rounded edges and two rubber grips on the side, which is the only thing holding it in place.

The Flir saves images at a very high resolution, but that is not a real advantage. Maybe cheat is too strong a word, but some sleight of hand is taking place here. The sensor is only capable of capturing 80 by 60 images. The device smooths and scales up the thermal image and combines it with a much higher-resolution visible light image from a second camera. This device adds two cameras to your phone.

It works despite being a bit stealth. The visible light camera adds a ghostly edge-drawn effect to the image that can be very useful when trying to figure out which part of a window is leaking warm air or which component on a circuit board is overheating.

It requires more power to be complex. The extra battery in the camera is located on the bottom of the device and needs to be charged through theusb-c port. The camera isn't working if you don't charge it. To turn the camera on, you have to press a button at the bottom of the device, then wait about 20 seconds for the app to detect the camera. It is one more device to keep charged, and the images you get are great, but it all feels overcomplicated compared to the other cameras.

The problem with thermal cameras is that they have to fit into the phone's charging port, which requires a tight fit. You might not be able to plug the device in fully if you have a case on your phone. A nice solution is to twist the wheel under the plug to make it move up and down to fit different phone cases. I had to use an extension cable or remove the case from my phone to use the Seek Thermal and Prime Perfect cameras. The Flir One Gen 3 was able to work with my Fold 4.