Jamming: promises, practice test and questions for the salesperson

Many salespeople promise “anti-jamming”. The only question that counts: what does the system do when someone really turns on a jammer? On this page: what we tested in practice, the gap between smooth sales talk and real-world behaviour, and three questions you should ask. Short definition first: what is jamming detection. Series context: Pitfall 4.

Guides · practice test

← Pitfall 4: jamming

The point. A jammer blocks the wireless signal of an alarm system. “Anti-jamming” on paper is not the same as: siren + alert on your phone under real interference. In our test the jammer fully disabled the standard subscription systems — as if the alarm were off, without the owner noticing. On our AJAX installs the siren and app alert did fire.

1. What is jamming?

A jammer is a signal jammer that cuts the wireless link between sensors, hub and phone. The system can look “normal” while nothing gets through. Full explanation and diagram: Pitfall 4 — jamming and signal interference.

This page goes further: what the door-to-door rep promises, and what the system actually does when a jammer is on. That is often a world of difference — especially with monthly subscription systems.

2. What we tested

In a controlled test we deliberately blocked the wireless traffic on 868 MHz — the frequency many wireless alarm sensors use. In plain terms: we did what a burglar does with a jammer — cut the link between sensors and hub. On one side: our AJAX installations (Grade 2 and Grade 3, subscription-free). On the other: the monthly subscription systems pushy door-to-door salespeople often bring to your door.

Standard subscription (our test)

Fully disabled

No siren. No phone alert. No contact with the monitoring centre. As long as the jammer was on, the whole subscription system was effectively off — without the owner realising.

Our AJAX install (our test)

On-site response

Interference detection, a siren that sounds, and an alert on your phone — without waiting for a call centre.

Conclusion from that test

Under active jamming the subscription system was effectively OFF, without the owner knowing. Brochure “anti-jamming” does not protect you then. What counts is what you see and hear in that moment — not the sticker on the box.

Without a working outdoor siren and without an alert on your phone, the neighbourhood hears nothing, the burglar is not driven off, and your belongings are very likely to disappear. That is exactly the risk of a subscription system that goes silent the moment someone turns on a jammer.

We install subscription-free AJAX systems and do not connect a monitoring centre. What you read here is what we saw in that test.

3. “We have jamming detection too”

You hear that sentence often. Without detail it means little. Press for:

  • Does the siren sound when the signal is blocked?
  • Do you get an alert on your phone — on your screen, not only “the monitoring centre will call you”?
  • Within how many seconds? Can they show or test that?

Sometimes subscription providers charge roughly €5 extra per month for a small black antenna. That is supposed to “detect” jamming via an external aerial. In practice: when a jammer is active, all relevant frequencies are jammed — including the band that antenna uses. You pay extra for something that makes no difference when it matters. The only sensible question remains: what happens now under interference — siren, app, or silence?

Modern jammers often hit several frequencies at once. Detection that only watches one band is then too thin.

Independent example — KTH Stockholm (February 2025). Cybersecurity student Joakim Öberg at KTH (Royal Institute of Technology) studied the wireless security of one of the largest nationally known alarm providers in Scandinavia. He looked at how sensors, hub and monitoring centre talk to each other over the air.

Finding: under jamming on the sensor frequency, the alert did not reach the hub. As long as the jammer was on, the system stayed silent — an intruder could walk in calmly. Only when the jammer was switched off did the alarm finally trigger. Supervisor Professor Pontus Johnson said customers should be informed about this risk. The provider pointed to “multiple layers of protection” and procedures for disruption attempts — but the core problem remained: no alert during active jamming.

Marketing language is not proof. More context: Pitfall 4.

4. Three questions for every salesperson

When someone promises “anti-jamming” — ask these questions, preferably with the app open:

  • 1. What do I see on my phone during jamming — and how fast? Not “the monitoring centre will call you”. What alert, on my screen, within how many seconds? Can you show or test that?
  • 2. Does the siren still sound if the hub is “deaf”? If not, one interference event can silence the noise. More: outdoor siren & jamming.
  • 3. Can you show live signal values in the app? Some systems show signal strength per sensor. Anyone who cannot show that has no transparent monitoring of the link.

Questions on ownership, monthly fees or monitoring protocol: Pitfall 1, Pitfall 2.

5. Frequently asked questions

  • Does jamming happen often?

    It occurs in targeted burglaries and with vacant homes. Whether it is statistically “likely” matters less than: what if it happens to you? Then you want the system to respond.

  • Are you saying subscriptions are always useless under jamming?

    No. We are saying “anti-jamming” on paper can differ from response in practice. In our test the jammer fully disabled the standard subscription systems we tested — no siren, no app alert, system effectively off.

  • Is AJAX perfect?

    No system is perfect. The difference in our test was large: subscription systems fully disabled by the jammer, siren + app alert on our installs — without a monitoring centre in between.

No obligation · at home · Costa Blanca & Costa Calida

Want to discuss jamming in practice?

At a house visit we explain what should happen under signal interference — and which questions to ask every salesperson about anti-jamming.

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More than 3,000 installations since 2019 · Google rating 4.8 · accredited Ajax Systems Partner

Next step: Grade 2 Baseline

On AJAX Grade 2 Baseline you can read what EN 50131 Grade 2 means and why it is the standard for most homes. Or go to the full overview.

AJAX Grade 2 Baseline → To the overview →