(Thanks to NoCamels) No need to get dirty or buy an expensive tyre pressure gauge. Download the TyreCheck app from Israel’s Neomatix and use your Smartphone to scan the tyres. If you need air, TyreCheck then tells you where to find the nearest air pump and the correct pressure.
http://nocamels.com/2012/10/never-check-your-tire-air-pressure-theres-an-app-for-that/
http://www.youtube.com/watch?v=HPFUaVhl76I&feature=player_embedded