I live in an apartment in far north phoenix (i-17+carefree hwy). i was sitting in my living room, around 7:15-7:30 pm, and i heard a noise, which turned out to be a helicopter. now, we have plenty of air traffic in our neighborhood, especially with a hospital down the street, but this was louder as it was closer and much lower to the ground. i'm always fairly alert and curious, but didn't make much of it until i looked out my dining room window, which has a clear view looking west/northwest towards lake pleasant. what got me out of my seat was white lights that were unaccountable by sound. i saw the red lights of what was clearly a helicopter and could hear it plainly, but it was following an object that appeared black and had three, constant, white lights in a very obvious triangle structure. the two came from behind our unit making their trajectory coming from the ne heading sw, but they were very low (maybe 100-200 feet, hard to tell at night). the object itself was maybe 50 ft from one light to the next, and it was an equilateral triangle. the triangle made absolutely no noise that i, or my fiance could hear as we were both watching at this point with naked eye and binoculars. they were moving very slow, even for a helicopter, maybe 20-30 mph. they moved this direction, toward the i-17 freeway, before turning nw heading towards ben avery range or just slightly east of that where it went behind the small mountains there. we followed them as they reappeared heading s/sw toward the peoria/glendale area. at this time they were likely over lake pleasant rd. or close to it. the object was still moving at the same slow pace, still being followed closely by the helicopter. during this whole thing, a couple more helicopters came into the area as well. we followed them as long as we could as they disappeared behind the mountains to the s/sw of us. this was definitely the closest and largest encounter i'd ever had and wish i was on my patio at the time as it would've been right in front of me and could've provided more details. honestly, i was quite excited the whole time and i'm still stoked today as i never felt like we were in danger, at all. i'm constantly looking out our windows and this time it paid off! i don't have any pictures, but since i'm an artist, i could probably make a drawing or two if need be.