Bosch Door/Window Contact II [+M]

The tiny magnet is a good reason to choose it

Bosch's Door/Window Contact II [+M] is more interesting on an awkward window than on an ordinary cupboard. Its magnet is only 3 mm thick, so the moving part can be discreet even when the sensor itself needs more room. The two pieces can sit up to 15 mm apart when correctly aligned. That gives you a useful option where a chunkier magnet would interfere with the frame.

The main sensor is a more visible 75 × 22 × 23 mm white block. Its IP45 housing also makes it worth considering for an outdoor opening within radio range. That broadens the choice of locations, although the frame still needs room for both pieces.

For a recessed frame that needs the magnet raised instead, Eve Door & Window includes spacers. Choose the mounting arrangement that fits the actual opening before choosing the app logo.

The button can make one sensor do two jobs

A button beside the door is a useful extra: it can become a light control or a trigger for leaving the house. Bosch includes button functions in its direct Matter feature list, although the chosen platform must expose them. It is worth paying for if one sensor can cover an opening and a frequently used action.

Bosch's own system adds a particularly thoughtful pause function. A double press can ignore one opening and closing, letting you take the dog out without triggering the normal window or door routine. Its ready-made alarm and ventilation services also stay in Bosch's system. Those are stronger reasons to use a Bosch controller than simply wanting to see whether a window is open.

The sensor uses either Thread for direct Matter or Zigbee for Bosch Smart Home. It does not run both radios as two simultaneous connections. Direct Matter needs a suitable controller and Thread border router; an existing Bosch system can use its own controller instead.

[+M] does not mean the security-focused Plus model

The similarly named Door/Window Contact II Plus detects vibration as well as opening. This [+M] version does not. If detecting someone disturbing a window before it opens is the priority in a Bosch alarm system, that difference should decide the purchase.

For ordinary ventilation or entry reminders, the simpler contact is enough. It reports separation from its magnet, so a closed reading does not prove that a door is locked. It also needs one replaceable CR123A lithium battery. Bosch's quoted battery-life figure was established with its own controllers; we would not budget on the same interval in every Matter home.

Buy it for a particular opening

Bosch's German store listed one white sensor at €44.95 and three at €124.95 on September 10, 2026, including VAT. The bundle saves €9.90 against three singles. That is useful once you know where each will go, but too small a saving to justify covering every window before trying one.

Keep a working older Bosch contact if it already handles the same routine. Buy [+M] when the thin magnet, button or ability to move to direct Matter will earn its place. For a plain indoor cupboard with none of those needs, start with a cheaper sensor that fits.