Singapore is one of the most humid inhabited places on Earth. The average annual relative humidity is 84%, and during the northeast monsoon (November-March) it regularly exceeds 90%. For smart home systems, this means that humidity sensors are not just a "gadget" — they are a critical piece of infrastructure that protects interiors from mould, corrosion and electronic damage.
How humidity measurement in the tropics differs from a temperate climate
Standard household sensors are designed for the 20-80% RH (relative humidity) range. In Singapore, humidity regularly exceeds this range, causing:
- Sensor saturation — readings "freeze" at 80% or show artificially low values
- Calibration drift — after 3-6 months of operation in the tropics, a cheap sensor can show an error of +/-10%
- Condensation on the sensing element — water condensing directly on the sensor causes readings of 99-100% even when the actual humidity is 85%
This is why using sensors with a capacitive sensing element is crucial in Singapore conditions — they are more resistant to saturation than older resistive sensors.
Tested devices — results from HDB flats
Aqara Temperature & Humidity Sensor T1
Protocol: Zigbee 3.0 (requires an Aqara hub or compatible one). Sensing element: Sensirion SHT40 — one of the most accurate capacitive sensors on the market. Declared accuracy: +/-1.8% RH in the 0-100% range. In our tests in a bathroom of an HDB flat in Ang Mo Kio (3 months of continuous measurement), the deviation from a reference laboratory hygrometer did not exceed 2.5%.
Power supply: CR2450 battery, lifespan 18-24 months in reporting mode every 5 minutes. Price in Singapore: 22-28 SGD.
SwitchBot Meter Plus
Connectivity: Bluetooth Low Energy + optional SwitchBot Hub Mini for WiFi integration. Sensing element: Sensirion SHTC3. Declared accuracy: +/-3% RH. The device is equipped with an e-ink display — useful for placing in a visible location (e.g. a shelf in the living room).
A significant drawback for HDB flats: Bluetooth range is 5-10 metres through a concrete wall. Without the hub, you cannot read data from a sensor placed in the bathroom while in the living room. With the SwitchBot Hub Mini (an additional 45 SGD), the problem disappears. Price of the sensor alone: 18-24 SGD.
Govee WiFi Thermo-Hygrometer H5179
Connectivity: WiFi 2.4 GHz (direct, no hub needed). Declared accuracy: +/-3% RH. Advantage: instant integration — just connect to WiFi through the app. Downside: consumes more energy than Zigbee/BLE sensors; AAA batteries need replacing every 4-6 months.
In our tests, the Govee H5179 showed a tendency to underread humidity by 3-5% in the range above 85% RH. The manufacturer confirmed that the sensor is calibrated for the 30-80% RH range. Price in Singapore: 25-35 SGD.
Optimal sensor placement in a flat
Based on our measurements from 12 HDB flats across various Singapore districts (Bishan, Toa Payoh, Ang Mo Kio, Woodlands), we developed the following placement recommendations:
- Bathroom: a mandatory sensor at a height of 120-150 cm from the floor, at least 50 cm from the shower. Avoid mounting above the door — steam accumulates there and readings will be inflated.
- Kitchen: the sensor is best placed in the cabinet above the sink (not directly above the stove). A Singapore kitchen with frequent high-heat cooking generates momentary humidity spikes to 95%+ — it is worth setting up average filtering (e.g. measurement every 5 min, alarm based on 30-minute average).
- Bedroom: on the bedside table or a shelf. In an air-conditioned room, humidity drops to 50-60%, but after turning off the AC it rises to 80% within 45-60 minutes.
- Wardrobes/closets: a small BLE sensor inside the wardrobe. In enclosed spaces without ventilation, humidity can reach 90%+ and cause mould growth on organic fabric clothing.
Automation based on humidity readings
A sensor without automation only provides information. The real value comes with integration with other devices. Here are proven automation scenarios tested in our conditions:
- Humidity > 75% in the bathroom: automatic activation of the exhaust fan (via a smart plug, e.g. TP-Link Tapo P110) for 30 minutes
- Humidity > 80% in the bedroom: activate the AC in Dry mode (dehumidification) — requires a smart IR remote (e.g. SwitchBot Hub Mini or Broadlink RM4)
- Humidity > 85% in the wardrobe: phone notification + activate an electric moisture absorber
- Humidity < 55% (rare, but possible with intensive AC use): notification about too low humidity, which can cause dry mucous membranes
According to data from the National Environment Agency (NEA), the optimal relative humidity for health and comfort in residential spaces is 40-70%. In the tropics, maintaining this level without active control is virtually impossible.
Calibration and maintenance
In a tropical climate, humidity sensors require calibration every 6-12 months. The simplest home method is the kitchen salt test: place the sensor in a sealed container next to a dish of wet salt — after 8 hours, the humidity should read exactly 75% RH (+/-1%). If the sensor shows a different value, you know the measurement error.
More about environmental measurement standards can be found on the National Environment Agency Singapore website.
