If you’re home alone, no cars in the driveway, and you want to take a shower, is it safer to keep entrance doors locked or unlocked? This question and the following discussion are important to read if you’re trying to kill time in front of a computer. The situation is highly dependent on numerous variables. For this example, we’ll make four assumptions:

1. the house is such that someone outside cannot tell if someone inside is showering.
2. the intruder is someone who tries to avoid being noticed by the occupants of the home but who, if confronted by an occupant, would kill them.
3. the intruder only has access to the inside of the house via the entrance doors.
4. it is daytime.

Option 1, lock the doors: you enter the bathroom, strip, run the water, showering phase begins. In the meantime, outside, potential intruder ‘A’ sees the driveway is empty of cars and takes this as a good indication that no one is home. Walks to the entrance door and finds it locked, further supporting the suspicion that no one is home (who locks themselves in during the day?). Convinced no one is home, the intruder doesn’t feel the need to be quiet about busting in and so has at the door with all manner of noise and force. Even with the shower going, you can hear a ruckus and quickly dry yourself and exit the bathroom to investigate. At about this time the intruder has made it through and enters the living quarters. You confront the intruder. You are dead.

Option 2, doors unlocked: you enter the bathroom, strip, run the water, showering phase begins. In the meantime, outside, potential intruder ‘A’ sees the driveway is empty of cars and takes this as a good indication that no one is home. Walks to the entrance door and finds it unlocked. This is at odds with the idea that no one is home, but it does allow the intruder to intrude very quietly, which they decide to do. Upon entering the living quarters, the intruder cannot help but notice that you are in the shower, but this presents itself as a huge opportunity: as long as they are reasonably quiet, they can steal as much as they like in the time it takes you to shower. The noise of the water flow, combined with your totally at ease and unsuspecting disposition, gives them good cover. As soon as they hear the water stop, they flea with the stolen goods, uninterested in a confrontation. You live.

Note: it is still possible to survive option 1. when you hear the sounds of door destruction, simply remain in the shower with the water running for a good five minutes. It would not be wise to shut the water off as soon as they get in the house, since they would not have had time to get their hands on anything, and fleeing empty handed is not something they would want to do, given the time they spent busting the door.