I am planning on making a electronic door lock with the Arduino. I have discovered that there are elderly and disabled people who have nurses come to their home to assist them getting out of bed. The only down side is that the front door would have to be unlocked so the nurse can get in and this poses obvious security risks. I will be making a keypad that is outside the front door so that the nurse can enter a code to get in. The code would only work for the time that the nurse is suppose to come for example 7:30 --> 8:30 if the nurse is suppose to be there at 8:00. There will also be a remote control that the disabled person can use to open the door in case of an emergency. I am pretty sure I have the electronics and programming down my only question is what mechanism can safely lock the door? I would like the device to be under 150$ obviously cheaper is better. I also don't want the device to look bad on the door although it can be over or attached to any part of it. The door would be a standard metal single front door. I would also prefer that the locking device be strong enough to prevent someone from kicking down the door.
Thank you for your help!