Motion sensor to flash a 12v light
That's not a problem and easy to do in 12V. Not only are 12V motion sensors readily available, they are about half the cost of 120V ones! 

I do not recommend running lamp power 150' at 12V.  I would have the 150' run be signal only (and power for the sensor[s]) and have a relay or electronic module operate the lamp proper.  The reason is voltage drop at that distance. A mere annoyance at 120V, it is critical at 12V.  

Voltage drop is proportional to actual current flowed, so keep that bare minimum on the long run.