It should be simple to construct an imitation security system by going onto
Ebay, buy a G4 12V red LED, G4 Bulb Holder and a small solar panel to trickle charge a 12V battery, approx 2AH capacity and some bell wire. Apart for fitting a solar panel, I have a similar setup for when I am fishing but it has a remote control built in and I have a white LED light instead, but I also bought a RED LED bulb as well to experiment with and I also keep my battery 1.4AH topped up with a solar panel when I am not using it. A larger solar panel would keep it going permanently 24 hours a day for years with no need for occasional top ups with a battery charger.
This way, no mains electric would be used, it would be a switch on and forget device. As for flashing, that would be another thing, whether you can buy a flashing red LED, rob the circuit board out of a cheap rear light and incorporate it into the system. But at the end of the day, it could be possible to use a rear light and modify it somehow.
In fact, just remmebered my remote control has various flashing modes, all controllable to how fast they flash etc