Ionization types use a battery to create a small current that charges the ion particles inside the detector. If that current is disrupted by smoke, an alarm is triggered. Though they are designed to detect all types of smoke, they tend to be more sensitive to smoke from fast-flaming fires, such as those that might occur in a kitchen. Another type is a photoelectric detector, which powers a small beam of light that, when broken by smoke, will sound an alarm. This type tends to be more sensitive to smoke from a smouldering fire, such as a burning cigarette on upholstery.
To be safe, homeowners are advised to use both types of detectors in their homes because no one can predict the type of fire that may break out, nor where it might start. Locate them strategically based on the type. Also, be sure your units are tested regularly, and their batteries are changed bi-annually.