ok2Martin
You buy a product 30 £, you have it for 30 £, it is logical!
Hide the power plant and the siren, make that nobody can reach the siren, the siren makes so much noise as we do not know where from comes the noise.
My system costs 3200 £ there are very visible devices, siren revolving light outside to inform the thieves and about invisible systems, impossible to neutralize.
But one day I would have the visit of thieves, it is the life ...................
The solution:
Three big well raised dogs and a crossbow with very sharp arrows