There are two different types of smoke detectors; optical and ionic. These detect fires in different ways.
Optical "looks"
Residential fires often start as smoldering fires in furniture and electrical equipment. A smoldering fire develops slowly and with smaller flames. An optical smoke detector "sees" the slightly larger particles in the toxic smoke that forms when a smoldering fire develops. With an optical smoke detector, you are more likely to be alerted early in the event of a smoldering fire.
Ionic "feels"
A fire with a high temperature and a lot of flames is often called a "high-energy fire". The smoke from such a fire contains ionic gas particles, which an ionic smoke detector reacts to. In homes, high-energy fires are not as common as smoldering fires.
Connect your alerts
Remember that you can connect the smoke detectors together so that all the detectors beep at the same time in the event of a fire. This is especially important if your home has several floors.
Look for the CE mark
It is the dealers who are responsible for ensuring that the smoke detectors they sell are manufactured in accordance with the regulations. What you need to check is that the detector is CE marked.