Why My Front Door is Always Locked.

So my husband always asks me why I lock the front door, even when I am home during the day, and today was an excellent example as to why I keep this habit.  I believe our front door has some sort of voodoo on it, it's possessed.  It sometimes opens on it's own, even if it's not that windy out.  My husband of course doesn't believe me but it's true.  I have seen or heard it happen several times.  Sometimes it opens if I have been using the door to our backyard (which is also always locked).  So, even though I didn't study physics I believe that there is some force field that is activated when the back door is opened which causes the front door to become jealous and open as well.  Crazy? I know!
Prime example: today, because it was so beautiful outside, Grace came home from school and immediately wanted to play outside in the melting snow.  Leah was up from her nap and of course wanted to join her sister, even though she can't walk yet and doesn't understand the whole muddy ice/water mixture that is happening in our backyard.  So Grace and my husband were out mucking it up in the backyard while Leah was watching them behind glass.  I was inside with my youngest, checking Facebook I believe.  Then I heard a car or truck, some sort of automobile drive by and thought, wow that's pretty loud to hear behind closed doors and went to check it out and found THE FRONT DOOR OPEN WITH LEAH OUTSIDE ON THE SECOND STEP!!!  Some how my ninja daughter opened the door, crawled down onto the landing and then down again onto our second landing (if you saw my house this would make complete sense but trust me, it was amazing that she didn't hurt herself).  Being the horrible mother that I am, I scooped my youngest up and brought her inside before any of the neighbours knew what had happened.  Once inside I locked the front door.  And that is why I lock my doors during the day, even when I am home.