The board does look like it has a set of contact pads on the bottom edge and can be separated from the main board. With a two conductor wire soldered between them. If desired.
The darlington transistor takes the small voltage from the contacts when wet and amplifies it. The transistor turns on the sounder. It has a DC gain of 30,000 {from a spec sheet.}
I ordered one of the kits today and will post findings when I get it.
Could you just use a pair of wires between the Powerflash's inputs to trigger it when wet. I kind of doubt it.
Would depend on how conductive the water was. So it could provied enough current through the inputs to trigger it.
An electronic circuit maybe needed to get the Powerflasher to trigger from a wet sensor.
I tried a Flood Stop Moisture Sensor from another experiment I was doing. Alone on the Powerflash's Input. It would trigger it sometimes but not 100% reliable. This was with the first 2" dipped in a cup of water.
http://www.getfloodstop.com/product_p/xs-01.htmI had used the amplification part of this project with the Flood Stop Sensor. Triggering an Insteon IOLinc but a Powerflasher may also be possible.
http://www.gardnerswebsite.com/ds10a/index.html
