I was cooking dinner and assumed he was on the computer in the living room. Went to find him when dinner was ready - no DS2. As I was about to go upstairs, I realised the front door was wide open. Rushed upstairs to check - no DS2 - came down, called DS1 and we both ran out into the road. I couldn't see him at all but then DS1 went haring off down the road (in his bare feet!) shouting 'I can see him Mum'. He was just rounding the corner at the end of the road - it's a cul de sac (thank God) which leads to a small park. DS1 found him standing at the gates saying 'open open'.
I am so with myself - I had left the door on the latch and the wind had obviously blown it open (DS2 can't open it on his own yet). And I am so proud of DS1! Not only did he come straight away when I called (something he doesn't always do...), he was the one to spot DS2, just from a tiny flash of red and run (like the wind) to catch him.
I've always been pretty laid back about DS2 because he hasn't ever got himself into potentially dangerouns situations. This was a real wake-up call.