If you have an existing porch light that works just fine, there's no need to replace it just because you want a motion sensor light. Instead, upgrade your existing fixture so it works as a motion detector light. Using a motion sensor light socket will turn your regular exterior light into a front porch motion light without requiring you to mess with any electrical wiring. Converting your existing porch light into a motion sensor light is as easy as screwing in a light bulb.
Remove the light bulb in your porch light. Grip the top of the bulb with a lint-free cloth between your skin and the bulb, then twist the bulb counterclockwise until it comes free of the socket.
Screw the motion light sensor into the socket where the front porch light bulb was before. It has a threaded socket just like your light bulb, making installation easy. Twist the motion light sensor clockwise until it's tightly seated.
Insert a light bulb into the socket of the motion light sensor. Using a lint-free cloth between your skin and the bulb, grip the top of the bulb and rotate it clockwise to secure the bulb in the socket.
Turn on your porch light switch and your motion light will activate when the sensor detects motion. It usually will turn off four minutes after the sensor stops detecting motion.