UEi PDT655 Differential Temperature Folding Pocket Thermometer, HVAC Digital Thermometer with Backlit Display and Magnetic Mount, Measures -58 to 572°F

The device is somewhat on the larger size, but for most users this is a plus. Its length is 6 inches and the width is 1.5 and it about ¾ inch thick. It will fit in a pocket but there will be no hiding it there, too long for that. However, it’s actually about ½ inch shorter that the Samsung phone I carry. The readout numbers are ¾ high and easy to read from 10ft away with good lighting. The display does light up, but only for about 4 seconds, just long enough to see the number if you’re in a dark basement or attic. The probe length is 5 inches and has enough mechanical resistance that it holds the position as you place it into a vent or hole. I was able to hang it onto a vertical return grill by the probe only, since in this case the grill was aluminum. The built-in magnets will hold it nicely on a flat metal area but probably not on a round duct. On those you could easily hang it by the probe though. It uses 1 CR2032 battery which helps keep the weight down. It’s a common enough battery that big box and drug stores sell them and they are cheap. It will self-power off after one hour, a nice feature, but it also means that any readings you have also disappear. It updates very quickly and follows the temp rise in a duct very near real time. It followed the rise I saw with my Fluke thermocouple and I was impressed with that. Accuracy seems reasonable and matches up nicely with other thermometers that I believe to be accurate. See photo

Used by pros for a reason. Easy to ready. Very handy.

These works great and it is bright when lit.

This thing isn’t a “pocket” thermometer by any means unless we’re going back to the early 90’s and JNCO jeans are back in style because those are the only pockets this thing is fitting in. It’s a decent thermometer to keep in your service bag but not in your pocket like all the other ones on the market. Also why can’t the backlight stay on for I don’t know like 30 seconds. Hell even a minute would be awesome. The backlight on this illuminates for 5-8 maybe 7 seconds at best. It’s damn near pointless.

My reason for the purchase is to measure the central air in my house. This thermometer responds very fast and reads me the temperature of the air realsed from A/C unit, which allows me to compare the reading to the temperature read on the wall thermostat. The light on the panel is clear so one does not need to struggle to read the measurements.