H-G5 is a simple GSM gate opener with one channel, which should be worked together with the eletronic lock. It's easy to install and even don't need professional person to do it. The manager can use the master phone number to setup 99 phone numbers that can unlock the gate or setup any phone numbers can unlock the gate. G15 can setup master password and sub-password for protecting. Just dial the SIM card number in the G15, the electronic lock will automatically open, no need any charges and it's very convenient for the user.