If your car remote has a dead battery or is just malfunctioning, you can still turn off your alarm with the key. Cars that have an alarm system also have a security system that matches a chipped key code to the car when you turn the ignition or put it in the door. If you have an aftermarket alarm, you may have to call the manufacturer for help, as the alarm system is not usually set to work with your car key.
Put your key into the driver's-side door lock. If you have a push-button key, you'll have to find the hidden key inside of it, which is used to get into your car if the remote isn't working. Look for a small button on the side of the key fob that you can press in with your fingernail or slide over to release a small key.
Turn the key in the door to unlock it. Some vehicles require that you turn the key to the left and some require you turn it to the right. If you hear the door unlock, your alarm is reset.
Open the door and put the key in the ignition if your alarm sounds from unlocking the door. Turn the car on. The ignition interaction will silence your alarm, as your vehicle recognises the key.
Consult your owner's manual or dealer if you have a push-button key or "smart" key, which is a key that does require traditional key turning to start the car. Sometimes these cars are paired with a driver's-side door that hides the key lock underneath a small panel to the side of the handle, which you'll have to take off.
Do not try this with an aftermarket alarm system, call the manufacturer or reference your owner's manual.