I have been watching documentaries on the Roman Republic/Empire with an interest on every day life lived by the Romans. I notice that they live in these apartments or even nice homes and shops were very common. How would people have secured their homes when they weren't there? Did they have locks or someone else who stays behind and keeps an eye on everything? I would think that these places would have made a target rich environment for thieves. Did they shop keepers just load up all of their merchandise and take it back home with them?
It should be noted that based on evidence from Pompeii and Herculaneum, in the vast majority of shops the shopowner or the person tending the shop, had living quarters in the back of the shop (or more frequently above the shop, with a ladder or stairs leading up to the living quarters from the shop). So it would be very rare occasions when a shop would be completely abandonded.
And that is also how the current consensus on the extant plaster cast of something resembling a wooden shutter door from a storefront in Pompeii is. The shutter is not actually a shutter, but sections of wooden planks linked by metal rings that could only be removed by a person staying inside.
So security in those cases was having someone stay behind in the shop, which would be comparably easier than today, since households were larger, and there could be slaves mending business or staying at home while the proprietor would be away.