An AED must be easy to operate. It uses voice prompts to instruct the rescuer. Once the user open the lid of the AED, the unit is turned on automatically. The rescuer will be prompted to apply two pads provided with the AED to the patient's chest. In order to minimize any potential user errors during the tense moments in an emergency situation, some AEDs have the electrode pads pre-connected to the device, with functional test performed daily. Non-side specific electrode pads will also allow the rescuer to affix them to the patient as quickly as possible, without any polarity restrictions. Once applied, the AED will begin to monitor the victim's heart rhythm. If a "shockable" rhythm is detected, the machine will charge itself and instruct the rescuer to stand clear of the victim and to press the shock button. Typically, fully automated or single button operated AEDs would be most desirable as it would minimize any error and confusion.