Leak detector/flow indicator

[PlainName]

I need to set up a water leak detector. There are apparently many available but they seem to listen out for the appropriate sound, or require insertion into the pipework. Neither are suitable for my purposes, which is basically to detect when the hose to the outside tap has worked its way loose. So, my requirements are:

1. Non-intrusive - don't want to be cutting into pipes and probably introducing new leak potentials

2. Non-acoustic - leak could be anywhere from under the lawn to down the side of the garage.

But.. I don't need to know the actual flow (although that would be cool if it were easily possible, it's not a necessity). So:

3. Detection of flow or no flow.

Are there any magic keywords that would help with a search?

[PlainName]

Seems the magic word is 'sensor' (as opposed to 'meter'). Anyway, non-intrusive seems to be ultrasonic and very precise setup. You can get a system (pair of sensors plus controller) for about £100 or pay £500 for a simpler clamp-on single sensor.

Decided to go with inline hall effect job for £11.