For testing purposes I use an old Android 2.3 device that runs an old version of Cyanogenmod. Unfortunately I could not find an option to enable ADB over network in the device’s settings. I am not a fan of plugging in the device every time I would like to debug an application. But, fortunately, there is a way to enable ADB over network via Terminal if your device is rooted:
su setprop service.adb.tcp.port 5555 stop adbd start adbd
Afterwards you can connect as usual by running
adb connect device-ip on your development machine.
To disable ADB over network you can set the TCP port option to
setprop service.adb.tcp.port -1 stop adbd start adbd