Do you have a multi function display? If so does it recognise the drivers door is open when lights are on and no key in the ignition? Mine has a faulty door sensor and doesn't always do this, therefore not beeping when it should.
Be careful as if this is the case it may not recognise you opening and closing the car door when you unlock the car, subsequently relocking the car after one minute. Fine if you're inside, but if not and you leave keys in it you are locked out!