How do store security cameras work?

I stole alcohol at the 7/11 down the street from my house. I was never caught with it, and this wasn't the first or last time I've stolen from the same isle of that store. Out of nowhere, my grandma was driving me to school, and she's like, "I don't like you hanging around Alisha. You were caught shoplifting with her at 7/11. The security cameras caught you." And that was like... wth. That had happened 4 months ago, and it had never been brought up. I had no idea I was ever caught. How did security identify me and contact my grandmother? And why was I not caught walking out of the store with alcohol underage, isn't that a little more serious than the shoplifting? The alcohol rack was right there.

Update: I understand that the security did pick me up. The problem is that I live in a city, where people aren't generally known, and I've made some changes to myself to the extent that if they saw any of my school photos since they were taken, it would not be identified as me. I do know some of the casheers, but this wasn't one of the people who I had ever seen before or would know my family. I don't know how they identified me, then contacted my grandmother, after the security picked me up. Also, why I wasn't punished by the security, the police, or my family- not only for shoplifting, but for posession of alcohol underage. That's something that would get sent to the police, I'd think.

cameras are EVERYWHERE these days... most are hidden in stuff rather than those big ones that sit in the store corners...
The camera records all movement and depending on the system, will keep the video of the customers/theives for up to a year. all it takes is a store owner with some time on their hands to go back and hit rewind... you are lucky - apparently the store owner knows your grandma and was kind to you!!
It should have been the COPS picking you up at school instead!!!

the people just didn't tell the cops because they get in trouble i don't know why it's in the rules the cameras get black and white video the people took a picture of the film with your face then the look into all of the schools in the area then the residential they got you identified told your gram then i guess she just didn't tell you it takes around two weeks to get the people found

the cameras go to the security department in the store and theres someone who watches them ! they either go from one spot of the store to another on one screen or several screens with a different spot or the store that they watch...thats alotta tvs