Perimeter Detect Circuit Examples


ZYMKEY and HSM security modules feature two independent perimeter circuits that can be configured to detect physical tamper intrusion events.

Electrical Requirements

Each perimeter loop should be connected with a 30 AWG wire or thicker and nominal length of 2 feet. For longer lengths contact Zymbit. The wire should be electrically insulated for all applications. A shielded cable may be necessary for electrically noisy or industrial applications.

Physical Circuit Connections

How these circuits are configured physically will vary depending upon the specific application, enclosure and security needs. Standard wires, custom flex PCBs and rigid PCBs may all be used to complete a perimeter loop circuit.

Here we share some practical examples of how to configure perimeter detect circuits for different applications and equipment.

To learn about software configuration and use of perimeter detect functions Learn more>


Direct Connect to HSM4 Hat

HSM4 HAT provides four pin header and FPC connectors to interface to perimeter circuits 1 and 2. This is convenient for rapid prototyping and small scale production situations.
For high volume applications, different connector types are available - contact zymbit for more details.

Perimeter HDR (Header) Pinout

Perimeter FPC (Flexible Printed Circuit) Pinout

HSM Direct Connector - Hirose Header DF40HC(3.5)-30DS-0.4V(51)

Direct Cable Connect to Zymkey 4i

Perimeter circuits on Zymbit 4i are accessed from a standard microUSB connector.

Use a standard microUSB extension cable to close circuits P1 and P2 as follows.

Adapter Connect to Zymkey 4i.

Several adapters are available from Zymbit that simplify connection from the microUSB to header and FPC. These are convenient for development. Buy Adapters >

Flexible Security Shield Wrapping RPi4

HSM4 Security Module, fitted to PiHat1. Flex circuit connects to FPC connector on HAT
Security Blanket Wrapping Pi4_

Rigid Security Shield installed on ProtoKit4

A printed circuit shield is fitted into the lid of the ProtoKit 4 and pogo pins connect the top mesh to the the bottom board. When the lid is closed, the circuit is closed.

The shield connects the following four perimeter signals available on the protoboard:

FlexCable Wrap with PiZero Hat

SDCard Blocking Perimeter Adapter with PiZero Hat

Tamper Switches & FlexCable with Secure Compute Device

Zymbit secure compute motherboard for RPi

Internal Tamper Switches

Secure Compute Device in 2U Rack with External Tamper Switches

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Great update! Thank you! I see the adapter module has been listed on the store, are there any plans to sell the security shield as well?

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Good to hear this was helpful.
We are making some general upgrades to the Protokit, including making the security shield available as an option. We will be sharing more information on this early March… stay tuned.

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Is the security shield now available as an option on the

@jason - not currently available on the 4S. But we have a new protokit being announced next month… we’ll keep you posted on that via email. How many of the shields might you need ?

What is the status of the security shield?

I am curious what the status is on the security shield. What would be nice is a complete enclosure that has the shield built in with pogopins and perhaps some way of detecting intrusion via a photodiode or photoresistor.

I am digressing, but having the ability to have an enclosure that has both normal screws, as well as a set of one-way screws wouldn’t hurt either, just so once it is put together for the final time, it stays that way for good.

I appreciate your work, as this is greatly helping with a number of IoT projects I’m working on, especially with edge device compromise a major issue.

@Jason @mlts22 we are close to releasing some solutions, similar to the security shield, but not the shield depicted in this thread.

It would be helpful to know what your general enclosure requirements are - size, material, environmental rating - feel free to post here, or send to if you prefer a private channel.


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