Fortress Interlocks

About Fortress:

Fortress Interlocks has a simple mission: to help businesses protect their human and capital assets.

We do this by designing and manufacturing safety interlock systems for industrial applications. These range from power generation, steelmaking and automotive manufacturing to food and beverage processing, materials recycling and construction.

Through the use of interlocks, our products ensure all activities are undertaken in a safe, predetermined sequence. This creates a safer workplace where employees are safeguarded from injury and equipment is protected from damage.

Our product portfolio includes trapped key interlocks (mGard), heavy duty safety gate switches, with and without guard locking (amGard Pro) and standard duty interlocks with in-built control functionality (tGard). All product ranges are compliant with the latest machinery safety standards and independently approved by TUV.


Because our products are modular, they can be adapted to just about any safeguarding scenario in just about any industrial environment. If one of our existing products can’t solve your problem, our extensive experience and know-how also allows us to provide bespoke products.

With over 40 years’ experience, we’ve become known in the industry for innovative design, robust engineering and reliability.

We are a member of the Machine Safety Alliance along with Festo, Pilz Automation Technology, Troax, UK Engineering, and Werma. The Machine Safety Alliance is a non-profit organisation that aims to share its collective knowledge and expertise and help companies understand and comply with safety regulations while balancing productivity.

Based in Wolverhampton in the UK, we have offices in the USA, the Netherlands, Australia, China and Brazil and a global network of trusted distributors and channel partners.

Fortress is a subsidiary of Halma plc. Halma is an international group of companies that make products for hazard detection, life protection, personal and public health improvement and environmental protection. Halma has nearly 50 businesses in 23 countries and major operations in Europe, the USA and Asia. It is a FTSE 250 company quoted on the London Stock Exchange.

Fortress Product Range:

amGardpro:  modular safety gate switch interlocks


  • The strongest interlock in the world
  • Highest level of actuator mis-alignment on the market
  • TUV approved to PLe
  • Safety key option prevents unexpected startup
  • Modular design allows flexible approach to machine safety

amGardpro is the ultimate range of safety gate switches, from Fortress Interlocks. The range has a unique modular construction which allows easy configuration and provides total electro-mechanical solutions for practically any safeguarding application up to SIL3 (EN/IEC 60261) Category 4 and PLe (EN/ISO 13849-1), as approved by independent test house TUV.

With its unrivalled design concept, amGardpro offers a range of fully integrated safety interlocks, including solenoid and non-solenoid safety switches complete with a host of additional options including key control modules, internal and escape release, redundant sensors, lock out/tag out and push buttons, estops and indication lights for enhanced functionality, all assembled in one device. The robust construction of this range makes it ideal for use in a wide range of industrial applications when safety, strength and reliability are of paramount importance.

The amGardpro system replaces all adaptions normally fitted within a guarding system, such that additional hardware like door catches, actuators, closing mechanisms, internal release mechanisms, key functions including authorised access and deadlocks are no longer needed. All of these separate functions can be incorporated into amGardpro configurations, resulting in the most flexible safety gate switch solution available for today’s industrial environment.

mGard – modular trapped key technology

Fortress1-mGard 1

  • Only trapped key interlock on the market with TUV approval to PLe
  • A trapped key system removes the need for wiring at the gate
  • Modular design allows multiple logic sequences (e.g. jog control or teach mode)
  • Broadest trapped key interlock range available on the market
  • Trapped key technology offer the lowest solution cost for retrofit

mGard is the premier range of trapped key interlocks for industrial safety applications, from Fortress Interlocks. Trapped key interlocking (often referred to as Castell locking) is a method of controlling two or more independent operations which must take place in a predetermined sequence. The need for this sequence may be safety to personnel and equipment, or it may be to control processes. It is, therefore, essential that the interlocking should be positive and incapable of defeat by unauthorised means.

It is called “Trapped Key” as it works by releasing and trapping keys in a predetermined sequence. As an example, after the control or power has been isolated on a machine, a key is released that can be used to grant access to individual or multiple doors OR after a switch disconnector has been opened in an electrical interlock scheme, a key is released to enable an earth switch to be closed and applied.

The principles of trapped key interlocking apply to all industries where it is essential that all energy sources are isolated before gaining access to machinery. Almost all safety issues can simply be solved by selecting the required products in order of the steps shown on this page.
Fortress trapped key interlocking is therefore a tried and tested method of mechanically safeguarding dangerous machines and hazardous processes, and is suitable for use in safety applications up to SIL 3 (EN/IEC 62061), Category 4 and PLe (EN/ISO 13849-1), as approved by independent test house TUV.

All Fortress Interlocks in the mGard range are robust and modular in construction offering maximum flexibility for designers and all electrical switches have a European, Canadian and North American approvals.

tGard – Integrated Control & Safety Interlock

  • Metal body construction at competitors plastic price point
  • Customisable as standard – select your elements to create your taliored interlock
  • Stylish design enhances the workplace aesthetics
  • Unrivalled choice of control options
  • Very easy to install – four fixings only

tGard is the new innovative approach to controlling access to hazardous machinery and equipment. It is a compact metal bodied system that enables the configuration of various safety products including electrical safety gate switches (with or without guard locking), mechanical trapped key interlocks, and electrical operator controls, either as separate devices or integrated into one device.

tGard offers “a customised safety solution, as standard” and is defined by a range of tGard elements, including selector switches, safety switches (solenoid and non solenoid), personnel keys (safety keys), emergency release, push buttons, estops, indicator lamps and a choice of operating handles for both hinged and sliding guard doors. These elements are simply selected and then assembled into a robust housing, suitable for mounting onto machine guarding, providing the user with an exact configuration specific to the application.

tGard is quick and easy to install and can be mounted directly onto a flat surface, doors or extruded aluminium profiles without the need for mounting plates or brackets. It is IP65 as standard and has been designed to be fully compliant with the new machinery safety standards.


ISO 9001:2008

ISO 14001:2004

OHSAS 18001


TUV SUD Functional Safety  – mGard

TUV SUD Functional Safety – amGardpro

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For enquiries call our UK office on +44 (0)1902 349000

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