I just got the hot water tank installed to complete the radiant slab in my shop that I built 4 years ago. Playing aorund the other day with my laser temp gun, I was able to pretty accurately pinpoint the tubes in the floor based on heat output.
This could be really handy if you need to section off part of a shop/house with slab heat with walls, or add anchors for a lift, etc.

Just thought I'd pass this along.

 

I used a video and a digital camera to photograph the area where I knew I would be installing a wall, but the thermometer is a good idea if you are working without a map or are into an unknown area.

 

Mop the floor with water and watch the pattern as it dries. Take a picture of it.

Steve

 

I took lots of pictures, too.
The mopping is also a good idea!