For $ 20, you can buy a great analog or digital tire pressure gauge. (bestride.com)
To check your tires, you will want to get a good quality tire pressure gauge, and use the numbers for air pressure that are located inside the driver's door frame. (drivesafer.com)
As a sanity check, I'd recommend buying a cheap, simple, mechanical tire pressure gauge to verify the values. (mechanics.stackexchange.com)