Wireless alarm systems have replaced traditional wired ones in most UK homes over the last decade, and for good reason, they’re cleaner to fit, more flexible, and the technology has caught up to (and overtaken) wired equivalents on reliability.
If you’re considering one for your home, here’s a plain-English explanation of how they actually work.
The three core parts
1. The hub (or control panel)
The hub is the brain of the system. It’s usually a small box plugged in somewhere central in the house. It listens for signals from all the sensors, decides what to do when something happens, talks to your phone via the internet, and can trigger the siren.
Most modern hubs have battery backup (so they keep working if the power goes out), Ethernet for internet, and a cellular SIM card as a backup, meaning if your broadband fails, they can still send alerts over 4G.
2. The sensors
Sensors are the eyes and ears of the system. Common types include:
- Motion sensors (PIR): Detect movement using infrared. Modern ones are “pet immune” up to a certain weight so your dog or cat doesn’t set them off.
- Door and window contacts: Two-part magnetic sensors that trigger when the magnet moves away from the sensor, i.e. when the door or window opens.
- Glass-break detectors: Listen for the specific frequency of breaking glass.
- Smoke and CO detectors: Fire and carbon monoxide sensors that also tie into the same system.
- Photo-verification sensors: Like a motion sensor but with a built-in camera that snaps a photo when triggered.
Each sensor sits on a battery and talks to the hub wirelessly. On modern systems like Ajax, those batteries last up to seven years.
3. The sirens
A loud noise both alerts you and deters the intruder. Most systems have an internal siren (inside the hub) and an external one mounted somewhere visible on the outside of the property. The visible external siren is a huge part of the deterrent effect.
How they talk to each other
This is where modern wireless systems really differ from older ones. Each manufacturer uses their own wireless protocol. The good ones are:
- Encrypted: Signals between sensors and hub can’t be intercepted or spoofed.
- Two-way: Sensors confirm they received commands, so you know everything’s working.
- Anti-jamming: If someone tries to flood the airwaves to block the signals, the system detects it and alerts you.
- Long range: Ajax’s Jeweller protocol reaches up to 2km in open space, so even large properties work fine.
Cheap wireless alarms cut corners on these features. It’s why a £150 DIY system and a £900 professionally-installed system can look similar on the box but behave very differently in the real world.
How you interact with it
Modern wireless alarms are controlled three ways:
- Smartphone app. Arm, disarm, see who’s armed it, check status, get notifications. This is how most people use the system day to day.
- Key fob. A small remote you can carry with your keys, with arm/disarm buttons.
- Keypad. A wall-mounted unit, useful by the front door, where you can type a PIN to arm or disarm.
What happens when an alarm triggers
Imagine a window opens at 2am when the system is armed:
- The contact sensor on the window detects the magnet has moved away. It sends a wireless signal to the hub.
- The hub checks the system state. It’s armed, and there’s no entry delay configured for that window, so this is a real intrusion.
- The hub triggers the internal siren and the external siren simultaneously.
- The hub sends push notifications to every phone with the app installed.
- If you’ve added optional professional monitoring, an Alarm Receiving Centre operator is alerted and can call you to confirm before contacting police.
All of that happens in well under a second.
Wireless vs wired: is wireless really as good?
Today, for almost every home, yes. Modern wireless protocols are encrypted, monitored for jamming, and use sensors with multi-year batteries. The hub still has a wired internet connection (with cellular backup) for off-site notifications. The only thing “wireless” about it is the link between sensors and hub, and that’s the bit you really don’t want to be running cables for.