It has been known since ancient times that smoke has a calming effect on bees. Guard bees and bees that are injured during a hive inspection release pheromones to send signals to the other bees to warn them of danger, but the smoke masks these chemicals, disrupting the colony's defensive response.
The smoke has another effect on the bees too - it causes a feeding response. This is because if the bees think there is a fire they will plan to leave the hive and they want to stock up on food first. When a bee eats honey its abdomen swells which makes it difficult for it to sting.
You should puff a little smoke around the entrance to the hive about 5-10 minutes before you open it. This starts the fire drill and they will hopefully be full of honey and unable to sting when you open the hive. Once inside the hive - you should smoke a little on the tops of the frames as you inspect the colony.
This traditional smoker is a stainless steel container with bellows attached in which you light a small fire. You can burn a variety of materials such as dried leaves, cardboard or tightly packed dry grass but it is important that the smoke is cold and does not burn the bees.
This smoker has a diameter of 10cm and has a protection frame.