All Boeing and Airbus planes are equiped with evacutation slides. They are in that part of the door that bulges out at the bottom.
In the United States, slides must be armed before the aircraft can push back from the gate. By arming the slide, when the door opens, the evacuation slide opens too. In the US, the flight attendant working the entry door, will make an announcment along the lines of "Flight attendants arm doors for departure."
On the A320 family, and I assume with other Airbusses, there is a handle that pops up out of the door. When that is pushed down, it arms the bottle in the slide pack so that when the door is opened it blows the slide.
On the 707, 727, and the 737, there is what is called a "girt bar" which is latched to the floor. By latching that to the floor, when the door is opened, it pulls the slide out, and it is then inflated.
On larger Boeings, there is an automatic slide arming device just like that on the airbus where the bottle in the slide pack arms.
Once an aircraft reaches the gate, the f/a at the door used for exiting the plane will say "Flight Attendants, de-arm your doors for arrival." At that time, the girt bar is raised, or the door is switched in to the "De-armed" position and the door will open with out the slide inflating.
Any other questions?
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