Ajax Signal Strength & ReX 2: The UK Installer's Radio Range Guide

If your Ajax detector shows two bars on handover, you have already booked the call-back. This guide is for UK installers who need to get Ajax signal strength right first time — what the Jeweller radio protocol will genuinely deliver on a real site, what noise floor and signal readings you should accept, and exactly when to stop moving the hub and fit an Ajax ReX 2 Jeweller range extender instead. Every figure below comes from Ajax Systems' own published specifications and is cited inline.

Ajax signal strength and ReX 2 range extender installer guide — Signal strength is a survey outcome, not a commissioning surprise — test before you screw anything to a wall.

What this guide covers

The published range: Jeweller reaches up to 6,550 ft (about 2,000 m) hub-to-device in open space — and far less through a building.
The weakest link rule: the usable range is set by the shorter-range device in the pair, not by the hub.
The numbers to accept: average noise below −80 dBm, three bars after an attenuation test, never one.
ReX 2 vs ReX: only ReX 2 Jeweller carries the Wings protocol, so only ReX 2 supports MotionCam photo verification.
The hard limits: up to 5 range extenders per compatible hub, and range extenders never chain to each other.

How far does an Ajax Jeweller signal actually reach?

Ajax devices communicate with the hub over the proprietary two-way Jeweller radio protocol at a maximum range of 6,550 ft (about 2,000 m) in open space, with no obstacles between the two aerials (Ajax Systems support). That figure is a laboratory ceiling, not a specification you can design a house to. Every wall, floor, metal shutter, mirrored wardrobe and parked vehicle between hub and detector attenuates the signal, and a reinforced-concrete basement or a steel-clad agricultural building can kill it entirely.

Jeweller uses GFSK modulation on the 868 MHz band — in the UK and EU the sub-bands are 866.0–866.5 MHz, 868.0–868.6 MHz and 868.7–869.2 MHz — at a maximum effective radiated power of up to 25 mW, with automatic power control and frequency hopping to step around interference (ReX 2 Jeweller technical specifications). Alarms from a detector behind a ReX 2 reach the hub in 0.3 s, and the hub flags a communication failure after 36 s of silence on default polling settings.

Why the weakest device sets the range, not the hub

The usable radio range between any two Ajax devices is limited by the shorter-range device in the pair. Ajax's own worked example: if an Ajax Hub 2 Plus Jeweller is rated at 6,550 ft and a KeyPad Plus Jeweller at 5,550 ft, the maximum possible link between them is 5,550 ft, not 6,550 ft. Design to the weakest device you intend to fit, not to the panel.

This is why the trade convention is to survey with a glass-break detector. The Ajax GlassProtect U Jeweller has the shortest Jeweller range in the catalogue at 3,250 ft (about 990 m), so a site that passes the signal test with a GlassProtect in hand will pass with anything else you hang on the system. If the design includes photo verification, you also need a compatible hub and an Ajax MotionCam U Jeweller on site to test the Wings channel separately — Jeweller bars tell you nothing about Wings.

What signal strength should you accept at handover?

Accept three bars after an attenuation test, an average noise floor below −80 dBm, and nothing less. Ajax's commissioning guidance is explicit: read Average noise (dBm) in the hub states — the allowable level is below −80 dBm — and check cellular signal strength of each SIM at two bars or better before you commit to a hub position.

Two bars is where installs go wrong. It is enough to pass a walk test on a quiet Tuesday and not enough to survive a customer installing a mirrored wardrobe, parking a van on the drive, or a neighbour fitting a 868 MHz device of their own. Run the Jeweller signal strength test with the detector in hand, spend two to three minutes at every proposed device position, then fix the device temporarily with tape and run the attenuation test before you drill. Reset the automatic transmitter power level afterwards.

Three Ajax site scenarios showing where a ReX 2 range extender is needed — Three site types, three different answers: reposition the hub, add a ReX 2, or go wired.

When do you need an Ajax ReX 2 range extender?

Fit a range extender when repositioning the hub cannot give every device three bars — not before. The correct order of operations is: move the hub, retest every device position, and only then add an Ajax ReX 2 Jeweller (white) or Ajax ReX 2 Jeweller (black). Moving the hub is free; a range extender is a line on the quote and another mains outlet to find.

The classic UK jobs that need one are detached garages and annexes across a yard, three-storey townhouses where the hub sits in a ground-floor cupboard, farm outbuildings beyond the main house, and commercial units where a steel mezzanine sits between the panel and the far end of the floor. In each case the fix is the same: put the ReX 2 where it still has a strong link back to the hub, and let it cover the far zone.

Two limits bite in practice. Range extenders communicate only with the hub — you cannot chain a ReX 2 off another ReX 2 to walk a signal down a long site. And a ReX 2 needs mains: it runs on 110–240 V at up to 10 W, with a built-in backup battery giving up to 24 hours with Ethernet disabled or up to 12 hours with Ethernet enabled.

ReX 2 vs ReX Jeweller: which range extender for which job?

Specify ReX 2 unless the system has no photo verification and never will. The original Ajax ReX Jeweller carries Jeweller only, so MotionCam detectors cannot sit behind it; ReX 2 Jeweller adds the Wings protocol and an Ethernet port, which is what makes photo verification work through it.

Feature	ReX Jeweller (35280)	ReX 2 Jeweller (35282 / 35283)
Jeweller radio range (open space)	Up to 6,550 ft	Up to 5,550 ft (about 1,690 m)
Wings protocol / photo verification	No	Yes — up to 5,600 ft
MotionCam detectors behind it	Not supported	Supported
Ethernet	No	1 × 8P8C, up to 100 Mbps
Photo delivery time to hub	n/a	18 s via Wings, 10 s via Ethernet
Devices behind one extender	Hub-dependent	Up to 199, hub-dependent
Security grade / standards	Grade 2	Grade 2, EN 50131-3, PD 6662:2017

The Ethernet port is the underrated part. On a site with structured cabling already in place, running the ReX 2 back to the LAN gives you a wired path for photos and cuts photo delivery time from 18 s to 10 s, which matters when a monitoring centre is making a police-response decision from the images.

How many range extenders can one Ajax hub take?

Compatible hubs accept up to five range extenders; the first-generation Hub (2G) and Hub (4G) accept one (Ajax hub comparison). That ceiling is per system, and range extenders count towards the hub's total device budget — a Hub 2 Plus supports 200 devices in total, five of which may be extenders.

Hub	Devices	Range extenders	Photo verification
Hub (2G) / Hub (4G) Jeweller	100	1	No
Hub Plus Jeweller	150	5	No
Hub 2 (4G) Jeweller	100	5	Yes
Hub 2 Plus Jeweller	200	5	Yes

Hub choice and extender count are the same decision. If a large site is heading towards two or three extenders, specify the Hub 2 Plus from the start rather than discovering the 100-device ceiling on a Hub 2 (2G) halfway through second fix. Our complete Ajax wireless alarm system guide covers the wider hub comparison.

How to survey an Ajax site for signal strength

Survey before you quote, not on the day of the install. The sequence below is the one that stops re-visits.

Six-step Ajax radio survey workflow from noise floor to handover — Six steps from noise floor to handover — run them in this order and the system stays quiet.

Interview the customer. Ask what changes are planned — mirrored wardrobes, metal racking, a van on the drive. Radio-opaque objects installed after you leave are the commonest cause of a device dropping out.
Site the hub, then read the noise floor. Mains, wired internet, decent cellular on both SIMs, out of sight. Confirm average noise below −80 dBm before anything else.
Walk the site with a GlassProtect. Two to three minutes at every proposed position using the Jeweller signal strength test. Test Wings separately with a MotionCam if photo verification is in the design.
Move the hub before you add hardware. If a zone fails, reposition the hub and retest every position — a hub move invalidates every previous reading.
Add a ReX 2 only where the hub cannot reach. Site it with a strong link back to the hub, on mains, at least 3 ft from the hub and from other devices.
Attenuation test, then fix. Temporarily mount, run the attenuation test, reset transmitter power, and only then screw the device to the wall.

Ajax also publish a radio communication range calculator, which is genuinely useful at quotation stage — it is the easiest way to show a customer why the extender is on the quote.

When radio is the wrong answer

Some buildings will never give you reliable radio, and adding extenders is throwing money at physics. Metal-clad hangars with steel racking, reinforced-concrete basements and plant rooms full of switchgear are the usual suspects. In those spaces the answer is to bring wired detection back to the radio network with an integration module: an Ajax MultiTransmitter Jeweller brings up to 18 third-party wired detectors onto the Ajax system on a single radio link, and our MultiTransmitter installer guide walks through the wiring.

One radio link into a difficult area, with the detection itself hard-wired, is far more dependable than five wireless detectors each fighting the same steelwork. It is also cheaper than the third site visit.

ReX 2 Jeweller specifications at a glance

Specification	ReX 2 Jeweller
Frequency bands (UK/EU)	866.0–866.5 / 868.0–868.6 / 868.7–869.2 MHz
Modulation / max ERP	GFSK / up to 25 mW
Alarm delivery time to hub	0.3 s
Communication loss detection	After 36 s (default polling)
Mains supply	110–240 V, 50/60 Hz, up to 10 W
Backup battery life	Up to 24 h (Ethernet off) / up to 12 h (Ethernet on)
Dimensions	6.42 × 6.42 × 1.42 in (about 163 × 163 × 36 mm)
Protection class / environment	IP30, IK06 — indoor use only
Warranty	24 months

All figures above are from the official ReX 2 Jeweller technical specifications.

Frequently asked questions

What is a good Ajax signal strength reading?

Three bars on the Jeweller signal strength test, held steady through an attenuation test, with hub average noise below −80 dBm. Two bars is a call-back waiting to happen; one bar is a fail.

Can I connect one Ajax ReX 2 to another ReX 2?

No. Range extenders communicate only with the hub. You cannot chain them to walk a signal down a long site — each extender must have its own good link back to the panel.

Does the ReX Jeweller support MotionCam photo verification?

No. The original ReX Jeweller carries the Jeweller protocol only. Photo verification uses the separate Wings protocol, which is supported by ReX 2 Jeweller but not by ReX.

How many devices can sit behind one ReX 2?

Up to 199, depending on the hub model and its overall device ceiling. On a Hub 2 Plus the system total is 200 devices including up to five range extenders.

Does a low battery reduce Ajax signal quality?

No. Ajax state directly that a low battery charge does not affect communication quality — if the link is unstable, look for noise, obstruction or a hardware fault instead.

How far apart should a hub and a ReX 2 be mounted?

At least 3 ft (about 1 m). Ajax advise against installing wireless devices closer than 3 ft to a hub or range extender, near large metal objects and mirrors, or beside routers, modems and power cabling.

Related guides

Order Ajax range extenders and hubs from Netview

Netview is an authorised UK Ajax stockist based in Leicester. The ReX 2 Jeweller, Hub 2 Plus and the survey detectors in this guide are held in stock for same-day dispatch, with trade pricing for installers. Build a system to your survey with the Ajax system builder, or browse the full range at netviewcctv.co.uk.

September 4, 2026 | View: 1 | By: netviewcctv.co.uk