I know nothing about security and cameras !

I work from home in a caravan at the back of the garden. I can't see the house from here and I have couriers visit every couple of days. It's been fine until now as they couriers all know I'm here, but each of the companies has changed personnel multiple times since Christmas and it might take a month of deliveries before I catch the new guys to tell them.

So I'm thinking of a cheap driveway alarm. I don't need it to have video (it would be nice if it's cheap enough) but I want it to be simple.

Anyone have any suggestions ? I can see dozens on Aliexpress but this will be in the open with little to no shelter from the weather and being white they are easy to see and nick off with !