Jamming in alarm systems: explanation, promises and what we tested in practice

1. Background: what is jamming?

A jammer (signal jammer) is a device that blocks wireless radio signals. The aim: to sabotage a wireless alarm system so that sensors can no longer send alerts to the hub or monitoring centre. The intruder can then break in while the system appears to be working normally.

Almost all alarm systems installed today are wireless. That makes installation easier — no cables through walls and ceilings — but it also means the system depends on a radio link between sensors, siren and hub. That is not a problem in itself, provided disruption of that signal is detected and met with a concrete response: siren, alert, frequency switching.

If that disruption is not monitored, wireless becomes a major security risk. Many consumers do not know jammers exist — or that “anti-jamming” on paper can be very different from protection in practice.

2. What we tested

The question is straightforward: what happens when someone uses a jammer? We simulated that in a controlled environment — with a wideband jammer comparable to equipment found in burglary cases. On one side, our AJAX installations (Grade 2 and Grade 3, with outdoor detection). On the other, the standard subscription packages customers most often mention to us as an alternative.

With those subscription packages we observed: no siren, no alert on the phone, no alarm at the monitoring centre. The system stayed silent for as long as the jammer was active. With our AJAX installations, the opposite: disruption detection, an autonomous siren and an immediate alert on your phone.

Our conclusion: a wireless system that does nothing on site during active jamming does not protect you in practice against targeted sabotage — even if the brochure mentions “anti-jamming” or the system is called “officially approved”. It comes down to what actually happens when someone tries it.

We install subscription-free AJAX systems — no monitoring centre. This page describes what we have seen and tested in practice. The results apply to the systems and conditions we explain further below.

3. During active jamming — what we tested

4. “We have jamming detection too”

Almost every subscription provider now sprinkles in phrases that sound technical but mean little without explanation:

Sometimes there is an optional module at extra cost. But the question is simple: what does the system do when the signal is blocked? Does the siren sound? Do you get an alert on your phone? You should be able to see that — not just hear it in a sales pitch.

Modern jammers can disrupt multiple frequency bands at once (multi-band / “full spectrum”). Older “jamming detection” that watches a single band is not enough for that.

In February 2025, Joakim Öberg, a cybersecurity student at the Royal Institute of Technology Stockholm (KTH), published a thesis on the wireless security of one of the largest nationally known providers in Scandinavia. He analysed how sensors, hub and monitoring centre communicate wirelessly. Conclusion: a jamming attack on the sensor frequency blocks the alert to the hub. The intruder can enter calmly while the system stays silent. Only when the jammer is switched off does the alarm trigger. Supervisor Professor Pontus Johnson stated that customers should be informed about this risk. The provider responded with “multiple layers of protection” and procedures for disruption attempts — but the core problem remained: no alert during active jamming.

More on these pitfalls: article 4 in our 6 pitfalls series.

5. Three questions every salesperson should answer

Ask these when a salesperson promises “anti-jamming”. If they cannot demonstrate it, that is an answer in itself.

• What happens during jamming — and can you show me? What alert appears on my phone, within how many seconds? Not “the monitoring centre will call you” — my own screen. Can you demonstrate now: what on my phone and what on site?
  
  Why ask: anti-jamming appears in brochures, but anyone who cannot demonstrate it proves it is missing or does not work as promised.
• Do you guarantee an alert when the signal is disrupted? Do you promise I get an alert if the wireless signal is sabotaged? Can you describe exactly how it works and show in the app what is being monitored?
  
  Why ask: you separate marketing language from real function — and force an answer about what is actually monitored.
• Can you show live signal values in the app? Some systems show signal strength and disruption values per sensor — updated live. Can you show that now in my own app?
  
  Why ask: live signal values cannot be talked away — anyone who cannot show them has no transparent monitoring.

Questions about monitoring centres, outdoor detection or subscription costs are on other pages in our menu — here the focus is jamming only.

6. Frequently asked questions