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

Real-time temp readings. Magnets on the back sticks to the duct. What’s not to like. Simple design. Love it

An accurate well made thermometer that is much larger than the common pocket thermometer. It will fit a pocket, alone. If you buy it, it might not fit your maintenance pouch.

The large display on these probes are much easier to read, as an residential hvac tech I use these probes several times a day checking TDs. The green backlight is nice also for dark spaces. These probes are accurate and react quickly to temperature change. Only issue I’ve had is I dropped one of them about 6’ to a garage floor and now part of the display doesn’t show.. my fault tho honestly

I use this for checking the split system in my home. It works perfectly and was recommended by the a/c technician that was servicing the unit. A no brainer if you are looking for something like this.

Only lasted a few months reading negative 40 degrees. Way off. changed battery too. get the regular one

In my tool bag everyday. Small and compact. Sharp probe fits in the smallest duct holes or flex. Magnet is a bonus feature. Buy two for quick differentials

Good thermometer if you need temperature differential.