The Best Thermal Cameras for Your Phone

The Seek Thermal Compact offers the highest resolution of the thermal cameras I tested, capturing 206- by 156-pixel images and a temperature range of  –40 to 626 degrees Fahrenheit (–40 to 330 Celsius). That's only a marginally higher resolution than the much cheaper Uni-T camera I’ve written about below. Also, the wider temperature range probably won’t be useful unless you are a refrigeration engineer or like to hang out in volcanoes. The Seek Thermal Compact has a smaller angle of view than the others; it captures a 36-degree-wide view, while the Flir and others capture about a 50-degree wide view. That means it acts more like a zoom lens than a wide-angle lens. That might make the Seek Thermal Compact more useful for some cases (such as hunting, where a tighter view makes it easier to track an animal at a distance) but less useful for others, such as capturing a thermal image of the side of a house to look for hot spots: You have to stand farther back to get the entire house in the frame.  

The camera is named the Compact, and it is a neat little package; only an inch and a half wide with a tough plastic case and a focus ring that shields the lens. It is easy to install: You just plug it into the phone's charging port, which holds it firmly in place. Its the only camera I tested with an adjustable focus. Most come with fixed focus, which means taking a picture of anything closer than a foot or so away will give you a blurry image, but the Seek Thermal Compact can focus down to a couple of inches away. Again, that is a mixed blessing: It is useful if you need to move closer to pick out a single overheating component on a circuit board, but focusing on thermal images is sometimes difficult because of the low resolution. 

The Perfect Prime IR 203 is the cheapest thermal camera I looked at, priced at about $130 for the Android version and $140 for the iPhone model I tested. It’s a decent thermal camera for the money, but the 80 by 60-pixel resolution is lower than the others. The images it produces have little detail. It’s fine to help find a hot spot in your house insulation, but you might struggle to tell a bear from the trees on a dark knight. The camera itself is a little bigger than the Seek Thermal Compact, with a protruding front lens that could get more easily damaged. One nice touch here: The camera comes with a Lightning port extender that makes it possible to use the camera with a phone case. It should work with any iPhone running iOS 12.2 or later. 

The companion app, called SenXorProViewer, is available for iOS and Android. It’s pretty decent, with a clear interface that shows useful things like the highest and lowest temperature in the camera’s view. As well as capturing both still images scaled up to 400 by 310 pixels, it captures video at a rather jerky 15 frames per second. The app also includes a couple of unusual modes: average and predictive. The average mode smooths out the sometimes grainy video by averaging several frames. That makes it less prone to noise and other glitches, and it makes the images a little smoother. The predictive mode tries to interpolate between frames to make the motion less jerky and reduce ghosting, but I didn’t find it made much difference in the resulting video.

The Uni-T UTI-120M is a small, compact thermal camera that fits onto the bottom of your phone. A small sleeve around the plug means that it works with most phone cases. This 2-inch wide device captures infrared images at a relatively low 120- by 90-pixel resolution, but it has a couple extra modes that work around the low resolution to make the results more acceptable. The blended mode combines thermal images with ones from the phone camera, but this was pretty useless: On my Samsung Fold 4, the thermal camera was at one end of the phone and the built-in visible light camera at the other. With the two cameras at opposite ends of the phone, there was too much of a parallax to combine the images into anything other than a blurry mess, except with distant objects where the parallax is barely noticeable. The picture-in-picture mode is more useful, adding a thumbnail of the visible light image from the phone camera to the corner of the thermal image. It isn’t as effective as the combined images from the Flir camera, but it serves to help you find a heat source in the low-resolution thermal image. 

There are some nice touches here: Uni-T includes a short extension cable that lets you use the camera away from the phone or connect it to a phone with a bulky case, although the camera worked fine with a thick case on my Samsung Fold 4. The company also includes a USB-C to mini USB adapter in the Android version so you can use the camera with older Android phones that lack USB-C ports. An included waterproof case makes sure the delicate infrared lens won’t get damaged in your tool bag.

The Thermal Mobile app is also pretty good, although I tested only the Android version. (It's available for iOS too.) The app offers features like tracking high and low temperatures in the image simultaneously: useful if you are testing a heat transfer device like a refrigerator.