I've seen these on Banggood and was interested but have never bought one.
https://www.banggood.com/search/car-parking-sensor.html  They have some on
their US site if you don't want to wait for shipping from china.

Harry are you looking for something that will warn you when you are driving
if someone is in your blindspot, like what is available in some new cars?
I rode in a rental with that and it seems like that would be quite helpful
in a vanagon but probably quite  a challenge to implement.

Edward

On Sun, Jun 4, 2017 at 9:08 AM, Dug Smith <dug@dugbert.com> wrote:

> I honestly don't remember where I got them, but it'd be something like:
> http://www.slickcar.com/reverse-backup-sensors.asp
>
> On 6/3/2017 22:50, Jared Planter wrote:
>
>> Can you share a URL to the set you purchased?
>>
>
> toodle pip,
> --
>       Dug Smith          | Terry Pratchett: It's almost
> (mailto:dug@dugbert.com) |  impossible to ride a rock and roll
> (http://www.dugbert.com) |  motorbike and stay on for three verses.
>