I have done the leaving the front door open all weekend thing too.
At the time I lived next to some seriously fierce bikers – some of their frequent guests were in the Hells Angels I was reliably informed. Anyway, on returning home I was accosted by a couple of frightening looking characters enquiring as to my intentions regarding entering the house. Suffice to say I was not ‘allowed’ in until my neighbour had confirmed that I did indeed live there.
The comments of my ‘guards’ went along the lines of ‘you never know who is who nowadays, you get all sorts of riff raff if you aren’t careful!’