Originally Posted by Pestle:
I just treated myself to a vintage spring-driven pendulum wall clock. It hangs near the door, above the sign-in clipboard (so's I won't get any more "What time is it?"s at drop off). When it chimes for 7am, I turn on the porch light and unlock the door. I think having the chime helps me remember "Am I open? No; the clock didn't go BONG BONG BONG BONG BONG BONG BONG." 
I get it totally... I have special alarm set on my cell phone for 7:29am Monday thru Friday only... ONE parent is scheduled to arrive at 7:30, the others not until 8 (contracted hrs). The alarm reminds me to turn on the fairy lights & turn off front porch light/unlock door lol.