Guys, whilst one hates shutting the door after the horse has gone, there are several affordable devices that could help prevent or deter theft, but it depends on your rapid response I suppose. September issue of MBM has a feature on such devices. At random, there is the Yacht Watch NMEA which can plug into your on-board GPS, send you a text message when it gets disturbed, and when you interrogate it via mobile, will tell you it's position. Price: £459 inc VAT from Compulogic. www.protectyourproperty.com
Like other units, this can monitor weather, bilge and battery power and send you info via on-board modem to your mobile. You can also plug in a range of other sensors. It uses on-board power so it might be sensible to install it's own dedicated power-pack.
Other units enable you to send commands which activate a loud siren and have their own dedicated power supply.
My investment totals almost £30K and although I have the boat well hidden, it is also not able to be visually checked by anyone, making theft a doddle. I am certainly looking into these "big-boat" devices.