Balancing dependable fire detection with fewer nuisance alarms

A smoke alarm must achieve a careful balance. If it is too sensitive, small amounts of cooking fumes, dust or incense smoke may cause frequent nuisance alarms. If it is not sensitive enough, its response to a real fire may be delayed.

At Hangzhou Deheng Smart Electric Co., Ltd., we control the alarm response threshold of our photoelectric smoke alarms within a target range of 0.110–0.165 dB/m. This internal control range is designed to provide consistent early warning while reducing unnecessary activations caused by light, temporary airborne particles.

What Does 0.110–0.165 dB/m Mean?

The sensitivity of a photoelectric smoke alarm can be expressed as the smoke density present when the alarm activates.

The unit dB/m describes how much light is obscured by smoke over a defined distance:

• A lower response-threshold value means the alarm is more sensitive.
• A higher value means more smoke is required before the alarm activates.

Our target range of 0.110–0.165 dB/m is intended to avoid both extremes. It helps prevent the alarm from being excessively sensitive while ensuring that it responds when smoke reaches the specified alarm threshold.

This is our controlled production target and should not be interpreted as the complete acceptance range specified by EN 14604.

How Is the Sensitivity Tested?

Smoke alarm sensitivity cannot be evaluated reliably by simply spraying smoke near the product. A controlled test environment is required.

During sensitivity testing, the smoke alarm is placed in a test chamber or smoke tunnel where airflow and aerosol concentration can be controlled. Test smoke is introduced gradually, and the smoke density is continuously measured.

The general process includes:

1. Clean-air verification
   The test equipment is checked before testing to establish a stable clean-air reference.

2. Controlled smoke introduction
   Test aerosol is introduced progressively under controlled airflow conditions, avoiding an uncontrolled burst of smoke.

3. Response-threshold measurement
   The equipment records the smoke density at the exact moment the alarm activates.

4. Sensitivity adjustment and verification
   The alarm is calibrated and checked against our target range of 0.110–0.165 dB/m.

5. Non-conforming product control
   Products outside the specified sensitivity range are separated for adjustment, further inspection or rejection according to the applicable quality-control procedure.

Consistent testing helps control variations in optical components, the sensing chamber, electronic circuits and assembly.

Why Photoelectric Detection?

Our smoke alarms use photoelectric sensing technology. Inside the sensing chamber, a light source and receiver are positioned so that the receiver normally detects little or no direct light.

When smoke particles enter the chamber, they scatter the light. As the particle concentration increases, the signal received by the sensor also increases. Once the calibrated threshold is reached, the alarm sounds.

Photoelectric alarms are particularly effective at detecting the larger, light-scattering particles commonly associated with smouldering fires. The basic operating principle is also explained by the National Institute of Standards and Technology.

Will Incense Smoke Activate the Alarm?

Light incense smoke that disperses quickly may remain below the alarm threshold. Our controlled sensitivity range helps reduce nuisance alarms caused by small, temporary concentrations of airborne particles.

However, incense is a combustion source and produces real smoke particles. If incense is burned directly below an alarm, placed too close to it, or used in a poorly ventilated room until smoke accumulates, the alarm may activate. This is normal safety behaviour—not necessarily a product fault.

No conventional photoelectric smoke alarm can guarantee that it will always ignore incense smoke while responding to every possible fire. Smoke movement, particle concentration, ventilation, room layout and installation distance all affect alarm activation. Research also shows that nuisance alarms depend on aerosol properties, concentration, airflow and the distance between the alarm and the source. NIST research

For better performance:

• Do not install the alarm directly above incense, candles or cooking appliances.
• Avoid directing smoke or strong airflow toward the sensing chamber.
• Maintain reasonable room ventilation.
• Never cover, remove or disable an alarm to prevent nuisance activation.
• Follow the installation instructions and applicable local fire-safety requirements.

How Do We Avoid Missing a Real Fire?

Sensitivity control is not only about preventing an alarm from activating too early. It must also confirm that the alarm is not too insensitive.

By controlling the response threshold within the specified range, we verify that the alarm activates once smoke density reaches the required level. Relevant EN 14604 evaluations also examine performance factors such as initial sensitivity, directional dependence, airflow, supply-voltage variation, environmental conditioning and response to representative test fires.

Our recommended models, including DH-001 and DH-101, are designed according to EN 14604 requirements. Relevant EN 14604 and RoHS documentation can be provided for customer evaluation, subject to confirmation of the applicable model and document status.

Consistent Sensitivity, Dependable Protection

With more than 20 years of manufacturing experience, Hangzhou Deheng Smart Electric Co., Ltd. provides OEM and ODM smoke alarm solutions supported by controlled production and quality-management procedures.

Our objective is straightforward: every alarm should provide dependable early warning without being unnecessarily sensitive in normal residential conditions.