The ABB Busch-Watchdog HF KNX (order code BMH/U2.1.1-885) is a 360° high-frequency presence detector for indoor KNX projects. 5.8 GHz radar penetrates drywall, wood, and glass — useful where PIR line-of-sight is limited.

This IP20 black-matt unit integrates a KNX bus coupler plus brightness, temperature, and humidity sensors. Two independent channels support constant-light switching, brightness-dependent lighting, and monitoring with KNX Data Secure.

Key Features

• 5.8 GHz HF radar: 360° detection through non-metallic materials; creep-under protection.
• 2 KNX channels: Independent lighting / constant-light control.
• Climate sensing: Brightness + temperature + humidity on the same device.
• KNX Data Secure: Secure commissioning for modern KNX installs.
• Flexible mounting: Recessed Ø 68 mm, surface housing, BS or VDE boxes with PMA adapters.
• IP55 sibling: For damp / outdoor-adjacent ceilings see BMH/U2.55.1. Outdoor PIR façade: BM/A4.1 Watchdog PRO 280°.

At a Glance

Specification	Detail
Product type	KNX HF presence detector, 360°, IP20
Order code	BMH/U2.1.1-885
Product ID	2TYZ510205G0701
Finish	Black matt (RAL 9005 similar)
Technology	5.8 GHz HF radar
Channels	2
Sensors	Brightness · temperature · humidity
Detection (circular)	Ø max. 10 m @ 2.5 m · 12 m @ 3.0 m · 10 m @ 4.0 m
Protection	IP20
Bus system	KNX TP · Data Secure

Product manual, installation instructions, CAD, EPLAN, and CE declaration are under Downloads.

Applications

• Offices & meeting rooms: Presence + constant light with climate feedback.
• Corridors behind partitions: HF sees through drywall where PIR cannot.
• Indoor IP20 ceilings: Recessed or surface with PMA accessories.
• Damp zones: Prefer BMH/U2.55.1 (IP55; brightness-only sensing).

Installation Notes

Cut a Ø 68 mm ceiling hole for recessed mounting, or use PMA/A1 surface / PMA/K box adapters. Connect KNX via the integrated bus coupler (no auxiliary mains). Commission with the ETS application from ABB documentation; follow the product manual in Downloads for range and sensitivity setup.