Propane level monitor

dometic makes one the size of a large pen. Has a rubberized tip on it that you place perpendicular to the tank. You push it in and if it runs red there is no propane at that area. Move it lower and try again, if it turns green you have propane at that level. Works great and I can use it on my propane grill at home. My parents bought 2 at an RV show in FL for $10 each. I know they were mismarked because everyplace else I see them they are $45 or so. Thats why they bought 2, it works great but at $45 I'm not sure I would have had them buy me one.