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Security Vulnerabilities Created By Key Switches

Key operated switches, commonly called "key switches", are used at many types of commercial and residential facilities. In facilities that have automatic gates, local regulations often require that a fire department key switch be installed to give emergency responders a way to gain access through the gate in an emergency. Many utilities, such as gas or electric companies, may also require that a key switch be provided to give their crews access to the site.


Even at facilities with card access control systems, it is common for customers to install key switches at exterior entrance gates to give employees an alternate means of entry using a key. Key switches are also used to control exterior overhead doors, operate elevators, and control equipment such as trash compactors or exterior fuel pumps.

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Example of Key Switches Used at Commercial Facilities


There are two types of key switches: switch locks, and mortise key switches.


Switch locks are self-contained devices that consist of a lock mechanism and a built-in electrical switch. Switch locks are compact units that can usually be mounted in a 3/4" hole. The limitation of switch locks is that they are available in only a limited number of keyways. This means that in most cases, they cannot be keyed to the building's regular key system, requiring that separate keys for the switch lock be issued to users.


Mortise key switches consist of two parts, a key switch mechanism, and a mortise lock cylinder. The advantage of mortise key switches is that they can be used with virtually any type of lock cylinder. This allows them to be keyed to the building's regular key system, letting users operate the key switch using the same key that they use at other doors.


The disadvantage of mortise key switches is that they are relatively large, requiring that they be flush-mounted in the wall or installed in a surface mounted box. Many mortise key switches use a standard single-gang or double-gang faceplate, allowing them to be mounted to standard electrical boxes.

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Example of Key Switches Used at Commercial Facilities


The Vulnerability


Key switches are simple electrical switches that provide either a normally-open switch contact, normally-closed switch contact, or both. In the majority of security applications, a normally-open switch contact is used. Anyone who has even a slight amount of electrical knowledge can bypass a key switch by simply removing it from the wall, and placing a jumper wire across the switch contacts. In most cases, this is easy to do, as standard slotted-head or Phillips-head screws have been used to fasten the key switch plate to the wall.


Many intruders are aware of the vulnerability of key switches and use the technique described above to commit burglaries. In many cases, the intruder reassembles the key switch after he has gained entry, so that the property owner may not even be aware that a burglary has occurred.


Recommendations For Improved Security


Silva Consultants recommends that the following steps be taken to improve the security of exterior key switches:

  • Confirm that the key switch is really needed in the first place. In some cases, key switches are rarely used, and the benefits of having them are outweighed by the security risks.


  • Use tamper-resistant security screws to mount the key switch. While not perfect, these screws provide some level of resistance and may discourage a less motivated intruder.


  • Flush-mounted key switches are more secure than surface-mounted key switches, so install them flush-mounted if possible. If the key switch must be surface-mounted, try to use an electrical box that has no 'knock-outs". (These can give an intruder access to the key switch wiring by removing a knock-out. ) If the box you are using does have knock-outs, permanently seal them by welding them or using epoxy.


  • If the facility has an intrusion alarm system, provide a tamper switch on the key switch and connect this as an input to the intrusion alarm panel. This input should be programmed as a 24-hour zone so that an alarm is generated regardless of whether the system is armed or disarmed.


  • For best security, use a Key Switch Lockout Circuit that automatically disconnects the key switch wiring whenever the key switch is tampered with (See diagram below.)


Key Switch Lockout Circuit


The circuit shown below provides an improved level of security for key switches. The circuit is designed to automatically disconnect the key switch wiring whenever the key switch is removed from the wall or electrical box. This circuit can be easily constructed using just a few simple electrical components and can be installed by your security systems integrator, gate installer, or electrician.

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Published May, 2016

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