Does anyone still use a home security system in their home? Need advice..?

I am considering to purchase a security system for my home, but I have a question regarding the use while I am in my home. If it is late a night and you want a late night snack, do you have to disarm it when you do get up or are the sensors a directed solely on the entrance of the house?
Update: I would love to get a dog, but there are times where I am away from the house for a long period of time.
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