I have one called automatic, it stays plugged in and monitors driving habits, mileage, trouble codes and does a google search for them automatically, etc. pretty good deal for $100 and you can get add on apps for it.
Another good thing is if it senses a crash it can send a text to anyone you choose and call for help if needed.
I got mine in the close out bin at Harbor Freight. It's a big handheld device that reads out the trouble codes and the part to examine in plain English.
They were dumping them due to a new, better model and had them for $14.95
I use a scan gauge 2 that's permanently installed through the OBD port on my powerstroke. Shows real time values while I drive. I've used it to check and clear codes as well. I think it was 100$.