Dr. Meter OBD2 Wi-Fi Code Scanner | $12 | Amazon | Promo code V7UY5UF7

You’ve heard of Automatic’s smart driving assistant, but if $130 is too rich for your blood, this OBD2 dongle costs over 90% less (with code V7UY5UF7), connects to any iPhone or Android device over Wi-Fi, and can fulfill many of the same functions using various third party apps.

The most obvious use case here is understanding and clearing check engine codes, but these things give you access to pretty much all of the sensor data in your vehicle, at a much more granular level than you’d get from all of the symbols in your instrument cluster.