Ajax Systems has become one of the most popular wireless alarm platforms in Europe. Its Jeweller 868 MHz protocol, AES-128 encryption, and cloud monitoring make it an excellent choice for residential security. Pairing Ajax with a KNX building automation system gives you something powerful: security events that trigger automation scenes, and KNX outputs that Ajax can monitor.

The integration challenge

Ajax is a closed ecosystem — it doesn't natively speak KNX. To bridge them, you have three main approaches: hardware relay outputs, webhook/API integration via Home Assistant, or Ajax WallSwitch as a KNX input source.

Method 1: Ajax output relays → KNX binary input

Ajax Hub 2 Plus supports output modules. The **Ajax Relay** (dry-contact output) can be wired to a KNX binary input (e.g. MDT BE-08230.01). When the Ajax alarm is armed or triggered, the relay closes, and the KNX binary input sends a telegram to your chosen group address. This triggers a KNX scene: arm → lower blinds, activate external lighting, send scene "secure". Trigger → flash lights, send alarm-output telegram to entry siren KNX actuator.

Method 2: Home Assistant as middleware

The most flexible approach: HA runs the Ajax integration (via hass-ajax or polling the Ajax Cloud API) and the KNX integration simultaneously. An HA automation bridges events: "when ajax.hub_state changes to 'armed_away', call knx.send on GA 0/0/10 with value True". No relay wiring needed. Supports bidirectional — KNX keypad arm/disarm commands can set Ajax arm state via HA.

Method 3: Ajax WallSwitch as KNX input

Ajax WallSwitch is a wireless smart relay (250V, 16A) that can be controlled via the Ajax app or button. However, it's not a KNX device. Bridging via HA is the only practical path.

KNX scenes triggered by Ajax events

The most useful integrations in practice are: alarm triggered → panic light scene (all lights on 100%, strobe on exterior), disarmed → welcome home scene, armed → all lights off + blinds closed + AC setback. These scenes turn a security system from passive to actively enhancing the building experience.

What we recommend

For premium residential projects: wire Ajax Relay outputs to MDT binary inputs in the KNX panel, and supplement with Home Assistant for bidirectional control and CCTV integration. This gives you hardware reliability (relay works without software) plus software flexibility (HA adds intelligence).