While outside my home looking roughly NNW, the object in question caught my eye when it crossed my direction of view. Right at the 12 o'clock position relative to where I was standing. Initially I dismissed it as a plane but it piqued my interest after I immediately realized there were no navigational lights and the second observed flash was at a distance that, to me, could not have been covered in such a short time by a commercial airliner. It was a flashing beacon of light with no other observable characteristics. Plain white, not exceptionally bright. No noticeable sound, but it could have been washed out by the noise of the nearby freeway. Sighting duration was too short to say for certain there was a pattern. In total 5 flashes were observed. 3 of them were evenly spaced over time. There was a short period where I'd have expected another flash as it would have happened if it were purely sequential. The flash resumed after this with the same rhythm until I lost it behind the trees obscuring my view.My guesses at prosaic explanations have fallen short of my observation, however it may still have a prosaic origin. Based on my past observations, it was far too fast to be a satellite flaring in the sunlight. It was certainly too fast to be an airliner unless it was in relatively close proximity. The lack of navigational lights and sound indicates it was, at the very least, non-commercial. Military craft or hobbyist's quadcopter cannot be definitively ruled out.