What to do immediately after the key breaks
The first step is to stop and avoid making the situation worse. Do not try to force the remaining piece to turn the lock, and avoid pushing anything inside. If part of the key is sticking out, it might look easy to grab, but using pliers or random tools can snap it further or damage the lock cylinder.
Instead, assess the situation. If you’re locked out, you’ll need access as soon as possible. If the door is already open but the key is stuck, you still need to fix it quickly to secure the property. Either way, this is where a professional locksmith becomes the most practical solution.