About 25 percent smaller than an iPhone, the self-contained plastic tester has a small recessed button on its lower face that serves as a tray to receive a few drops of used oil – we used the dipstick. Sensors measure the capacitive and resistive properties of the oil (the lubricant degrades with use and the changes cause a variance in capacitive and resistive properties) and then score the fluid with a number between 1-10, indicated with an illuminated LED. Oil with a low score is still good, but oil with a high score is contaminated and needs replacing.
In practice, the Lubricheck ($39.95) seemed to work as well as promised. We tested a handful of cars, a lawnmower and a pressure washer, and the scores all appeared to be spot-on with the known life of the oil. We liked the size of the device, how simple it was to execute the test and how quickly the results appeared (less than a minute). Our only complaint was that the user needs to be careful to not drip oil into the unprotected slide switches - easier said than done when shaking oil off a thin metal rod (we accidentally got oil in the ON/OFF switch, but apparently to no ill effect).
Overall, the little plastic device impressed us, and it appears to provide consumers the information they need to extend oil change intervals. Of course Lubricheck isn't as accurate as spectroscopy, flash point, viscosity and chemical-based oil testing – we will still mail samples to Blackstone Labs for that.