Sensors

Smart home sensors — what they do and how they work

Smart home sensors are devices that monitor home conditions and notify the owner via an app or trigger automatic responses. A door sensor sends an alert when someone enters while you are away; a smoke sensor sends an alarm to your phone even when you are far from home; and a humidity sensor can automatically start a humidifier. Every sensor is an autonomous device powered by a battery or rechargeable cell, with no cable runs required.

Smoke and carbon monoxide sensor — Meross CS11

Carbon monoxide (CO) is dangerous precisely because it is colourless and odourless. Meross CS11-EU is a combined smoke and CO sensor certified to EN 14604 and EN 50291. It notifies with a loud 85 dB acoustic alarm and via the Meross app on iPhone and Android. It supports Apple HomeKit, enabling automations: for example, when smoke is detected other HomeKit devices can be triggered, and critical notifications (bypassing silent mode) appear on iPhone.

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

PIR motion sensor — automatic lighting and security

PIR (Passive Infrared) sensors detect changes in infrared radiation caused by the movement of a person or animal. Available at homescreen.pl:

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

Motion sensors integrate with lighting: they turn a light on when you enter a room and switch it off after a set period of inactivity. A natural application for hallways, bathrooms, pantries and garages.

Meross MS600 — mmWave presence sensor (Matter)

Meross MS600 is a different class of device from a classic PIR. It uses millimetre-wave (mmWave) radar technology, which detects even a stationary person sitting at a desk. A classic PIR misses someone who is sitting still — MS600 will not. It supports Matter, so it operates 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 opening sensor

An opening sensor consists of two parts: a magnet and a radio unit. When the distance between them increases (the door opens), the sensor sends a notification. Uses:

• Phone alert when the front door opens while you are away
• Automatic air conditioning switch-off when a window is open
• Notification when a child opens a medicine or alcohol cabinet
• Alarm schedule input — opening at 3 AM triggers sirens

Available: 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 the dishwasher, washing machine or in the bathroom can cause serious damage before it is discovered. A flood sensor is placed on the floor near the appliance — when the contact electrodes touch water it immediately sends an alarm to your phone. Meross MS400H supports HomeKit, while BlitzWolf BW-IS5 and BW-IS9 work over ZigBee via a gateway. The cost of a sensor is a fraction of the cost of flooding a neighbour or replacing flooring.

Temperature and humidity sensor

Monitoring indoor climate is useful not just for comfort. Too low humidity (<30%) promotes drying of mucous membranes and respiratory infections. Too high (>60%) promotes mould growth, especially in bathrooms and on external walls. Available models:

• BlitzWolf BW-IS4 and BW-IS8 — ZigBee, e-ink display with current reading
• Meross MS130-EU — WiFi with display and schedules
• Meross MS100FHHK — HomeKit, no display, for iOS automation integration
• 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 advantage of ZigBee is very low power consumption (a CR2032 battery in the Sonoff SNZB-03 lasts 1–2 years) and no WiFi network load. A ZigBee gateway supports up to 50–100 devices simultaneously.

WiFi sensors (BlitzWolf BW-IS7, Meross MS130) connect directly to the router without a gateway, but battery life is shorter. Meross MS600 Matter operates locally via WiFi without the cloud, giving response times below 100 ms.

Home Assistant integration

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

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

FAQ — Frequently asked questions

How does the Meross CS11 smoke and CO sensor work?

The smoke sensor detects combustion particles via a photoelectric chamber (light scattering change). CO detection uses an electrochemical sensor reacting to carbon monoxide concentration in the air. When the alarm threshold is exceeded, an 85 dB acoustic alarm sounds and a push notification is sent via the Meross app. CS11 supports HomeKit, so notifications arrive as "critical alerts" on iPhone, bypassing silent mode.

Which sensor to choose for a flat?

For basic safety: a smoke and CO sensor (Meross CS11) in the living room and bedroom, 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 children's room.

Do ZigBee sensors work without the internet?

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