When locked by fob, have to unlock by fob, using the key will set the security alarm off, but if a new battery just installed and no lights or anything works, check the battery for connections and voltage, if lights work and will not start and acts like the battery in fob is dead, unhook the negative terminal and let it sit, or go ahead and remove both and let it sit awhile, usually 5 to 15 minutes is long enough but depends on how much in the system needs to drain and reset.
go longer to be safe.