I want to detect all the android phone connected to my network by a wi-fi. I have used nmap but it is not showing any specific detail to get the android .can any thing is there by which I can detect at least a android is in my network.
Only give a cert/key to devices that "register" with IT.
You shouldn't have unauthorized devices on your network.
Use MAC address vendor lookup and record all the MAC address prefixes for all the phone manufacturers that use Android. It's a heuristic but a pretty good one.