The SA node generates an electric signal that normally travels down a specific path to reach the ventricles of the heart. A pacemaker is a device that changes the pattern of the heart's contractions by generating its own electrical impulse. A pacemaker uses batteries to send electrical impulses to your heart to help it pump properly. An electrode is placed next to your heart wall and small electrical charges travel through the wire to your heart.
Most pacemakers turn themselves on and off as needed.
Since your pacemaker generates its own electrical signal, you need to be aware of things in your surroundings that could affect that electrical signal. You should always carry a walled I.D. card with you, and let any medical or dental personnel know that you have a pacemaker before any procedure. They have shown not to damage pacemakers. Some common household devices have the potential to inhibit an occasional single beat. This is generally not a problem.