It is the most common Smoke Detector used today . It detects smoke by using either two principle of fire – 1- Light Obs-curation , 2- Light Scattering . It works best at smokes originating from fire producing large particle during combustion .

Spot type photoelectric smoke detectors using the light obs-curation principle have a light emitting device, usually a light-emitting diode (LED), a smoke chamber, and a photosensitive device that receives the light directly from the light source and produces a monitored current.
Smoke that enters the smoke chamber reduces the intensity of tech light reaching the photosensitive device, which reduces the monitored current. When the intensity drops below a certain level, the sensor control circuitry detects a drop in the current produced by the photosensitive device. When the current falls below a preset threshold, the smoke alarm is triggered.
Spot type photoelectric smoke detectors that use the light scattering principle are constructed similarly to the detectors that use the light obs-curation principle except that the photosensitive device is set so that it cannot see the light source directly. When smoke enters the chamber, the smoke particles reflect the light from the source into the photosensitive receiver. When sufficient light intensity is detected, the alarm is triggered.

Photoelectric Smoke Alarms operate using a light source , a light beam collimating system and a photoelectric sensor . After smoke reaches the optical chamber and while crossing the path of the light beam some of the light is scattered by the smoke particle , directing it to the sensor and activating the alarm .
These type of alarm detect visible fire particle sooner ( associated with slow smoldering fires ) sooner than Ionization alarm and hence these alarms respond best to the slow smoldering fires .

Advantages of Photoelectric Smoke Detectors:
Sensitive to visual particles of smoke
Detects smoldering low heat fires
Provide early warning

Disadvantages of Photoelectric Smoke Detectors:
Early contamination by dust causing reduced sensitivity
Detects presence of smoke, not toxicity
Must be cleaned on a regular basis
Has a potential for high false alarm rate

Typical locations or hazards for photoelectric detection:
Office areas
Clean rooms
Raised floor spaces
Atrium’s and corridors
Meeting rooms
Computer rooms
Telecommunications rooms
Electrical equipment rooms
Sleeping rooms
Storage closets