If the “ready” light is not on, that means that a zone is open. The keypad will show you which zone is open. Either a window or a door or perhaps something is in the way of a motion detector. First you should make sure all doors and windows are closed. If you cannot close a zone and get the “ready” light, you may bypass the problem zone. Please check your user manual to find out how to bypass a zone on your keypad. Bypassing an open zone will allow you to get the “ready” light and thereby arm the remainder of the zones.