Here is another compact device that can help you figure out when you are not sober. The BACtrack C8 uses the BluFire fuel cell sensor to estimate your alcohol level. It can also tell you when your BAC will return 0%. The BACtrack C8 has a portable design and optional Bluetooth connectivity.
The companion app saves your BAC results over time. It has rideshare integration, so you can call an Uber directly from it. The BACtrack C8 is available for under $100 at this time.