Sensors

Smart home sensors — what are they for and how do they work?

Smart home sensors are devices that monitor conditions in your home and notify you through an app or trigger automatic responses. A door sensor sends an alert when someone comes in while you are away, a smoke detector sends an alarm to your phone even when you are far from home, and a humidity sensor can automatically switch on a humidifier. Each sensor is a stand-alone device powered by a battery or rechargeable cell, with no need to run cables.

Smoke and carbon monoxide detector — Meross CS11

Carbon monoxide is dangerous precisely because it is colourless and odourless. The Meross CS11-EU is a combined smoke and CO detector certified to EN 14604 and EN 50291. It alerts you with a loud 85 dB sound signal and through the Meross app on iPhone and Android. It supports Apple HomeKit, which enables automation: for example, when smoke is detected, other HomeKit devices respond automatically and critical alerts appear on your iPhone (overriding silent mode).

The detector is mounted on the ceiling or a wall — mains-powered or battery-powered. It is especially recommended in homes with a gas boiler, fireplace or gas heater. The Meross CS11 detects both open fire (smoke) and slow CO poisoning from leaking heating systems.

PIR motion sensor — automatic lighting and protection

PIR (Passive Infrared) motion sensors detect changes in infrared radiation caused by the movement of a person or animal. Example models:

• BlitzWolf BW-IS3 — ZigBee, rechargeable, 110° detection angle, 7 m range
• Sonoff SNZB-03 — ZigBee, CR2032 battery, miniature, for wardrobes and drawers
• Meross MS600 — Matter WiFi presence sensor, mmWave technology

Motion sensors integrate with lighting: they switch a lamp on when you enter a room and turn it off after a set time without movement. This is a natural fit for hallways, bathrooms, pantries and garages.

Meross MS600 — mmWave presence sensor (Matter)

The Meross MS600 is a different class of device from a classic PIR. It uses millimetre-wave radar (mmWave)technology, which detects even a motionless person sitting at a desk. A classic PIR would miss someone sitting still — the MS600 will not. It supports Matter, so it works locally without the cloud and integrates with Apple Home, Google Home and Samsung SmartThings. Ideal for a home office where you want the air conditioning or lighting to respond to presence, not just movement.

Door and window sensor

A contact sensor is a pair: a magnet and a unit with a radio. When the distance between them increases (the door opens), the sensor sends a notification. Uses:

• A phone alert when the front door opens while you are away
• Automatically switching off the air conditioning when a window is open
• A notification when a child opens a cabinet with medicines or alcohol
• Part of an alarm schedule — an opening at 3 a.m. triggers the sirens

Example models: BlitzWolf BW-IS2 (ZigBee), BlitzWolf BW-IS6 (433 MHz), Meross MS200H (HomeKit) and Meross MS200, Sonoff SNZB-04 (ZigBee).

Flood and water leak sensor

A water leak under a dishwasher, washing machine or in the bathroom can cause serious damage before it is discovered. A flood sensor is placed on the floor next to the appliance — when its contact electrodes touch water, it immediately sends an alarm to your phone. The Meross MS400H supports HomeKit, while the BlitzWolf BW-IS5 and BW-IS9 work over ZigBee via a gateway. A sensor costs a fraction of what flooding your neighbour's flat or replacing a parquet floor would.

Temperature and humidity sensor

Monitoring the climate in your home is not just about comfort. Humidity that is too low (<30%) dries out mucous membranes and encourages respiratory infections. Humidity that is too high (>60%) encourages mould growth, especially in bathrooms and on external walls. Available models:

• BlitzWolf BW-IS4 and BW-IS8 — ZigBee, e-ink screen with a live reading
• Meross MS130-EU — WiFi with a display, schedules
• Meross MS100FHHK — HomeKit, no display, for integration with iOS automations
• Sonoff SNZB-02 — ZigBee, miniature, no display

Protocols: ZigBee, WiFi and Matter

Most BlitzWolf and Sonoff sensors use ZigBee, which requires a gateway (Sonoff Zigbee Bridge, BlitzWolf BW-GW1 or Aqara Hub). The advantages of ZigBee are very low energy consumption (the CR2032 battery in the Sonoff SNZB-03 lasts 1-2 years) and no load on your WiFi network. A ZigBee gateway can handle up to 50-100 devices at once.

WiFi sensors (BlitzWolf BW-IS7, Meross MS130) connect directly to the router without a gateway, but their battery lasts less. The Meross MS600 Matter works locally over WiFi without the cloud, giving a response time below 100 ms.

Integration with Home Assistant

All the sensors mentioned integrate with Home Assistant. ZigBee sensors via a USB ZigBee adapter (Sonoff Dongle Plus or ConBee II), Tuya and eWeLink sensors via the appropriate HACS integrations, and Meross Matter via the native Matter integration in HA 2023.5+. In Home Assistant you can create automations linking sensors with any devices: a flood sensor cuts power through a smart plug, a CO sensor triggers sirens and sends an SMS via a GSM integration.

Other automation devices: IP cameras for monitoring, smart plugs, switches, LED strips, home automation.

FAQ — Frequently asked questions

How does the Meross CS11 smoke and CO detector work?

The smoke detector senses combustion particles using a photoelectric chamber (change in light scattering). CO detection is handled by an electrochemical sensor that reacts to the concentration of carbon monoxide in the air. When the alarm threshold is exceeded, an 85 dB sound signal and a push notification via the Meross app are triggered. The CS11 supports HomeKit, so notifications arrive as a "critical alert" on iPhone, bypassing silent mode.

Which sensor should I choose for my home?

For basic safety: a smoke and CO detector (Meross CS11) in the living room and bedroom, and a flood sensor under the dishwasher and washing machine (Meross MS400H or BlitzWolf BW-IS5). For access control: a front door sensor (Sonoff SNZB-04). For comfort: a temperature and humidity sensor (Meross MS130) in the bedroom or child's room.

Do ZigBee sensors work without internet?

App notifications require internet. However, automations stored locally in the ZigBee gateway or in Home Assistant work without internet. Example: the Sonoff ZigBee Bridge Pro will trigger an alarm or send a local alert even without a cloud connection if the automation is configured locally via MQTT or eWeLink Scene.