IEMI and the physical attack surface of a business site.
Intentional electromagnetic interference (IEMI) is radio or pulse energy aimed at electronics to disrupt or damage them. On a business site the exposure sits in three places: the radio links a system depends on, the cables that leave the building, and what each door and recorder does when its electronics stop.
- Sheet
- Guide
- Published
- 21 October 2026
- Last updated
- 21 October 2026
- Written by
- Gentex AU
What IEMI is.
The term and its definition come from the IEC 61000 electromagnetic compatibility series.
The IEC defines IEMI as the intentional malicious generation of electromagnetic energy to introduce noise or signals into electric and electronic systems, disrupting, confusing or damaging them. It belongs to the wider family of high-power electromagnetic (HPEM) threats. Lightning and switching surges are its accidental relatives.
Sources come in two kinds. Narrowband sources put out a strong signal on one frequency, the way a jammer does. Wideband sources put out short pulses across many frequencies at once. Both lose strength quickly with distance, so where the electronics sit is part of the defence.
Australia prohibits the supply, possession and operation of mobile phone, GNSS and Wi-Fi jammers, and the ACMA enforces it. That makes jamming an offence. It does not make it impossible.
Energy gets in three ways.
- 01 Through the antenna.
- A radio picks up energy at the frequency it is built for. Wi-Fi cameras, wireless alarm detectors, wireless locks and a 4G alarm communicator all listen on a radio, and a strong signal on that frequency drowns them out. This is the cheapest attack, and the one most sites are exposed to.
- 02 Through the cable.
- Every cable is an unintended antenna. A long unshielded run picks up energy and delivers it as a voltage at the port it plugs into. The cable to an outdoor camera, a gate reader or a second building is the longest and most exposed run on most sites, and it ends in the rack beside everything else.
- 03 Through a reachable connection.
- Energy can also be put into a cable directly where an outsider can reach it: an external power outlet, or the network cable behind a camera on a carpark pole. That is a conducted attack. It needs physical access, which is why the reachable ends of the cabling are part of the attack surface.
What it does to security equipment.
The three levels of effect, from the one that passes to the one that does not.
- 01 Interference.
- The link drops while the signal is present and returns when it stops. A Wi-Fi camera leaves a gap in the recording. A wireless detector cannot report.
- 02 Upset.
- The device locks up or reboots, and stays down until it is power-cycled. This is the effect that matters most for doors, because a controller that stops falls back to whatever its locks do without it.
- 03 Damage.
- Ports and power supplies are destroyed. It takes far more energy at far shorter range. The protection that stops a lightning surge reaching a port also limits it.
Plan for the quiet failure. A jammed detector that cannot report looks the same on the panel as a quiet night, unless the panel treats lost supervision and radio interference as a fault.
What limits it.
- 01 Cable the positions that matter.
- A cabled camera or detector has no radio to jam. Keep wireless for positions that cannot be cabled, and know which ones they are. Our data cabling page covers the cable those positions run on.
- 02 Fibre for runs that leave the building.
- Fibre carries light, not current, so it neither picks up nor carries electromagnetic energy. A run to a second building, a gatehouse or a far yard pole on fibre cannot deliver a surge or an injected pulse into the rack.
- 03 Surge protection where copper enters.
- Copper that comes in from outside passes a surge protector bonded to earth at the point it enters the building, not where it lands in the rack. AS/NZS 1768 covers lightning protection.
- 04 Distance and walls for the rack.
- Field strength falls quickly with distance. A comms cupboard in the middle of the building, behind block or concrete, is harder to reach than one on the wall shared with the carpark or the next tenancy.
- 05 Supervision on every wireless device.
- Set the panel to report a detector that stops checking in, and radio interference, as a fault that is sent to monitoring. A jam that is reported is an event. A jam that is not is a blind spot.
- 06 Two paths for the alarm signal.
- An alarm that reports only over 4G can be silenced by a jammer. One that also reports over the wired internet has to lose both. Our commercial alarm systems page covers monitoring.
- 07 A chosen fail state for every door.
- Every electrified lock either releases or stays locked when its power or its controller drops. The access control page sets out fail-safe and fail-secure, and why the choice is made door by door.
- 08 Power that holds through a reset.
- A UPS behind the recorder, the switch and the door controller turns an upset into a reboot, not an outage, and the recording carries on.
Walk the site with this list.
Each line is something you can see or ask about on site. None needs test equipment.
Eight checks
- Every wireless device, by location: camera, detector, lock, keypad and alarm communicator.
- For each one, what the panel or recorder shows when it stops talking, and whether that reaches anyone.
- Every cable that leaves the building, and whether it is copper or fibre.
- Surge protection where copper enters, bonded to earth.
- Where the rack is, and what is on the other side of its walls.
- The fail state of every electrified door, written down.
- What runs on the UPS, and for how long.
- Whether the alarm reports by more than one path.
Send a floor plan or a site address. Enquiries are read Monday to Friday, 07:00–16:00.
The standards behind it.
- 01 IEC 61000-1-5.
- High-power electromagnetic effects on civil systems: what HPEM and IEMI do to ordinary electronics, and the language used to describe it.
- 02 IEC 61000-2-13.
- The HPEM environments themselves, radiated and conducted, that equipment may face.
- 03 IEC 61000-4-36.
- IEMI immunity test methods for equipment and systems. This is the standard to ask a manufacturer about if a site needs test evidence.
- 04 ITU-T K.81.
- A high-power electromagnetic immunity guide for telecommunication systems, including how to assess the risk to a site.
- 05 AS/NZS 1768.
- Lightning protection, including surge protection on the power and data lines that enter a building.
What we do not do.
We do not test equipment for IEMI immunity. That is laboratory work, done in a shielded chamber to IEC 61000-4-36, and it belongs to the manufacturer or a test house. A site that needs that evidence, such as a utility or a data centre, should make it a purchasing requirement.
What we do is the site side: the cable, the rack, the doors and the alarm, installed so that what each one does when it fails is chosen and written down. The same thinking applies to the network those devices sit on, which our briefing on securing IP cameras and access controllers covers. Where we support the site afterwards, that is IT services.
Questions we get asked.
Is IEMI a real risk for a small business?
Can a jammer stop a cabled camera?
Does shielded cable stop IEMI?
Are wireless alarm detectors safe to use?
Related sheets.
- IT services Networks, firewall rules, updates and support once the systems are in.
- Securing IP cameras and access controllers The network side of the same devices: segments, logins and firmware.
- Access control Readers, locks, and what each door does when the power fails.
- Data cabling The cable, the rack and the UPS that everything above runs on.
Walk the site with us.
Send a floor plan or a site address. We attend, look at what is there and tell you which of these checks it passes.
- To
- Gentex AU · Tullamarine VIC
- Reply
- Phone or email, usually the same business day
- Attending
- Mon–Fri 07:00–16:00
- Licensing
- Victorian Private Security Licence