I did this right in front of my next door neighbors and they never knew.
A few years ago my son bought me a blower/vac from Sears. It is a Craftsman. I really enjoy having it because it makes cleaning the driveway a breeze with all of the evergreen trees we have here in the Pacific northwest. I have found that the vibrations of the blower while running can be very enjoyable when held against my cock. I usually hold it with one hand and let it rest against my cock while it runs. I would love to do this until I cum but the bulge is obvious. I have a rather large cock and it is obvious in my jeans when it is hard. I don't mind if the neighbors see but I don't want to be obvious.
Well one day I decided to try the vacuum part of the blower. I put it together following the instructions. I had spent the day raking up leaves and branches in the yard and had several piles to clean up. My neighbors were out in their yard and doing some work too. Their rather hot 17 year old daughter was sun bathing in her bikini on the side porch. Well, I started up the blower vac and put the shoulder strap over my shoulder and started sucking up the leaves. It worked great. But it had an extra benefit. The blower was resting right on my cock. The longer I ran it the harder I got.
I was loving this. I was having loads of fun jacking off right in front of my neighbor, his wife and daughter, and they had no idea. The blower vac and the bag on it hid my cock from their view. I had to reach into my pants at one point to straighten things out but the blower vac hid it all. I kept sucking up piles of leaves trying not to go to fast. I wanted this to last. Finally I couldn't resist it any longer. I got that great feeling of my balls clenching and I shot at least 5 or 6 spurts into my pants. I shoot a lot and I had a really big wet spot to try to hide when I was done. It was great especially with the neighbors only 15 feet away. If they only knew.