If master keys belonging to a master key locking system are lost, an up-to-date locking diagram must be obtained from the manufacturer, and is (usually) only available with the owner’s permission. The locking diagram is used to assess the existence of keys and their hierarchy, and an investigation is instigated to determine whether more keys are missing. Should this be the case, and should there be no reasonable explanation as to why these keys are missing, it must be assumed that the current master key locking system is no longer secure.

As far as the insurer is concerned, loss of a key only requires the replacement of that particular key. If all keys are accounted for, the locking diagram is used to identify the required locking cylinders, half cylinders, knob cylinders etc. and get replacement quotes from suitable manufacturers. The value of the system to be scrapped is deducted from the best quote on offer.

In the case of a claim settlement under liability insurance, a new-for-old deduction is made using a current calculation basis of a total life span of 20 years for a master key locking system. Provided there are no other additions or deductions, the result of this calculation will be the amount of the insurer’s liability.

If required, one could consider a part- or total change to the system by using electronic or mechatronic locking cylinders

Diagram of central locking system

Diagram of master key system

Combination central lock and master key system