Sensorly Shows Where the 4G Really Is (3G too)!

I've seen it fill in when I drove in an unmapped area. I have vague memories having to choose 'live update' or something off a menu. I'd check the menus out. Or someone with better memory than me might come along and be specific.
 
Now if I'm not mistaken for this to actually work, and map out the locations, we have to leave the screen on and just let it dim? If we actually tap the power button to shut the screen off it won't map our area's even if you have it set to run in the background?
 
Checked their website.

"4G maps : green indicates 4G is available. Unlike other types of wireless networks, Android phones currently do not report how good 4G reception is so it cannot be plotted at this moment."

Even with that said I have full strength 4G and it shows blue not green....

Thought this would be a good app.