Can't find android device using “adb devices” command

Question

I am developing Android application on macOS and my application runs well on the emulator. I want to run it on the device, but when I run adb dev

Answer 1

If you're struggling with such an issue using Lollipop (Android 5.*) probably you guys should do one simple step that I'd done before my ADB (I use Ubuntu) got my phone:

Change USB PC connection type to "Send images(PTP)" (before I've been using "Media device(MTP)")

Just like this:

And don't forget to activate checkbox "USB debugging".