The Flir One Gen 3 is the largest of the thermal cameras I looked at; it’s about 2.6 inches wide and 1.3 inches tall, and it fits a lot into that space, including a built-in battery and two cameras. It is also the most complex of the cameras I looked at. This large camera body has rounded edges and two rubber grips on the side and a USB-C plug on the top that fits into the USB-C port (the iOS-ready version has a Lightning plug), which is the only thing holding it in place.
The Flir saves images at a remarkable 1,440 by 1,080 pixel resolution, but that’s a bit of a cheat. Well, perhaps cheat is too strong a word, but some sleight of hand is going on here. The infrared sensor only captures 80- by 60-pixel images. To create the higher resolution image, the device smooths and scales up the lo-res thermal image and combines it with a much-higher-resolution visible light image from a second camera located right next to the infrared one. Yup, this device adds two cameras to the multiple ones your phone already has.
It may be a bit sneaky, but it works. The visible light camera adds a ghostly edge-drawn effect to the image that can be very useful when trying to pinpoint a heat source—such as which side of a window is leaking warm air or which component on a circuit board is overheating—because it provides a visual map.
The downside of this complexity is that it requires more power. To handle this, Flir includes an extra battery in the camera, which you must charge through the USB-C port on the bottom of the device. If you don’t charge it, the camera doesn’t work. You also have to turn the camera on by pressing a button at the bottom of the device once you have plugged it in, then wait about 20 seconds for the Flir One app (available for iOS and Android) to detect the camera. The images you get are great, but it all feels overcomplicated compared to the other cameras, and it is one more device to keep charged.
The problem with this (and the other thermal cameras) is that they plug into the phone’s charging port, which requires a tight fit to work. If you have a case on your phone, you may not be able to plug the device in fully. The adjustable plug here is a nice solution, though; twisting the wheel under the connector makes it move up and down, providing an adjustable length to adapt to phone cases of different thicknesses. To use the Seek Thermal and the Prime Perfect cameras, I had to take the case off my phone or use an extension cable because the case blocked the plug from clicking fully into the phone’s socket. However, the Flir One Gen 3 worked with the rather chunky Samsung case on my Fold 4.