This is a pretty cool image illustrating where the leak is (you can see the smoke in the image on the left) and how the leak location is identified using the dye (shown in image on right).
The Smokewizard GLD-50 is the lightest, smallest smoke detector on the market, a great value when on a budget. It also features smoke volume (flow) control for easier leak detection. This unit is OEM-Approved. Small and Lightweight: 10″ x 5″ x 8.5″ – under 7 lbs. Visit Smoke Wizard GLD-50
for more details.