Alarm system disarmed

I used to feel secure sleeping home alone at night, knowing that Lucy was just in the next room and likely to bark relentlessly at anything that moved. My sense of security left this morning, though, when I watched from the living as a man, who I hope works for the gas/electric/water company, walked through the backyard and out again without Lucy uttering a single, sleepy growl. Perhaps she's only armed at night.