I lost my phone and used Android Device Manager to lock it. However, it turns out my boyfriend was last logged into my Gmail, so his phone is the one that was locked and now I can't remember the password!
How can we unlock his phone?
Only solution,Hard reset your phone and do a reset factory settings in recovery mode. BTW which phone model you are using, I guess it must be Samsung :)
One more way, if you know your phone is rooted and ADB on.. You have to delete all your key files from system folder. Try this. Connect you device with usb and run following command. If you are not able to do so, i am afraid. You need a full wipe.
adb devices adb shell cd data/system su rm *.key
Even if shows lock screen after reboot, try a easy random pattern/password.
sorry that is probably too late, but I found a solution. You have to sign in to a SAMSUNG account, and there is an unlock feature. If it doesn't work the first time, locked it with a 4 digit pin from the same Samsung page, in the cell enter the code and the lock will be temporarily removed but the screen lock will still be in place, so then again Unlock it from the Samsung tool.
I had the same problem on my LG Nexus 4. I just logged into Android Device Manager and set another password. No need to remember the old password!