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IoT Sensors 101: Temperature, Humidity, Motion and Contact Sensors Explained
IoT can sound complicated, but most practical projects for homes and small businesses rely on a handful of simple sensors. Understanding these four basic types will help you plan projects, talk to vendors and avoid buying the wrong device.
Temperature sensors
Temperature sensors are the most common IoT device. They are used in server rooms, cold rooms, kitchens, warehouses, greenhouses, offices and homes. Some measure air temperature, while probe sensors measure inside freezers, liquids or soil.
Things to know:
- Place air sensors away from direct sunlight, aircond vents and heat sources unless that is what you want to measure.
- For fridges and freezers, use probe sensors with the main unit outside, since cold drains batteries.
- Decide how often you need readings. Every few minutes suits cold rooms; less often suits offices.
For food businesses, temperature monitoring is often the first project worth doing. See our guide on cold chain basics for F&B SMEs.
Humidity sensors
Humidity sensors measure the amount of moisture in the air, usually as relative humidity. Most are combined with temperature sensors. In Malaysia's climate, humidity matters for mould prevention, product storage, comfort and equipment health.
Uses include monitoring warehouses storing paper, textiles or electronics, checking storerooms prone to mould, and managing dehumidifiers. Humidity sensors can drift over time, especially in very humid environments, so occasional comparison with a reference meter helps.
Motion sensors
Motion sensors detect movement, most commonly using passive infrared, which senses changes in heat patterns. They trigger lights, alarms, occupancy counts and automations.
Common pitfalls:
- They detect movement, not presence. A person sitting still may not be detected.
- Fans, curtains moving in aircond flow or pets can cause false triggers.
- Glass blocks passive infrared, so sensors do not work through windows.
- Mounting height and angle affect coverage, so follow the maker's guidance.
For office occupancy uses, our article on meeting room occupancy sensors explains how to combine motion with other data.
Contact sensors
Contact sensors, also called door or window sensors, use a magnet and a reed switch. When the two parts separate, the sensor reports open. They are cheap, reliable and long-lasting.
Uses include security alerts on doors and windows, checking whether freezers or cold room doors are left open, monitoring cabinet access and triggering lights when a store room opens. They are one of the best value sensors for small businesses.
Tip: contact sensors on fridge and cold room doors are often more useful than people expect. A door left open is one of the most common causes of temperature problems.
Choosing power and connectivity
Most of these sensors run on batteries and use low-power radios like Zigbee, Bluetooth, LoRaWAN or Thread. Some use Wi-Fi but drain batteries faster. Check expected battery life, how the app warns you about low batteries and whether batteries are easy to buy locally. Our guide on choosing IoT connectivity helps match radios to your site.
Installation tips that apply to all sensors
- Label each sensor with its location and purpose.
- Record installation dates and battery changes.
- Test alerts after installation, not when there is a real problem.
- Mount sensors securely so cleaners or staff do not move them.
- Review data after a week to spot placement issues.
Starting a project with basic sensors
A good first project combines one or two sensor types with a clear goal. Examples include temperature and door sensors on a freezer, motion and contact sensors for after-hours security, or temperature and humidity sensors in a storeroom. Measure the problem before and after so you can show the benefit. Then expand.
How often should sensors report?
Reporting frequency is a balance between detail and battery life. A freezer sensor reporting every few minutes catches a door left open quickly. An office temperature sensor reporting every fifteen minutes is plenty for comfort tracking. Motion and contact sensors usually report only when something changes, which saves power. When setting up, choose the slowest reporting rate that still lets you act in time. You can always increase it later for a specific problem area.
Beyond the basics
Once you are comfortable with these four, you can explore other sensors such as water leak detectors, air quality sensors measuring CO2 or particulate matter, energy meters, vibration sensors for machines and level sensors for tanks. The principles of placement, power and testing stay the same.
FAQ
Do I need a hub for these sensors?
It depends on the radio. Zigbee and Thread sensors need a hub. Wi-Fi sensors connect directly to your router. LoRaWAN sensors need a gateway.
How accurate are cheap temperature sensors?
Many are accurate enough for trend monitoring. For regulated uses, choose sensors with stated accuracy and calibration certificates.
How long do sensor batteries last?
It varies by device and reporting frequency, from months to years. Check the maker's estimate and monitor battery levels.
Learn these four sensors well and you will understand most practical IoT projects. Start small, place carefully and let real data guide your next steps.