The Bird Crash Preventer is a curtain of monofilament (fishing) lines spaced 3" apart that covers the exterior of a window. No assembly required. 

Its curtain rods are 3/4" square metal tubes held by brackets -- two brackets above and two below the window. The lines are factory-fastened and wound on one rod. You simply unroll the length needed to cover your window (up to 84"). Only four screws to install. Available in 3-foot and 4-foot wide models.

Its proven effectiveness without obstructing views make it the best all-around product on the market.