So you want to make a player detector well you came to the right place! In this blog i will explain 
what you will need to make the player detector and how it works. Also this does not work in survival
because we will be using a special block called, "Command Blocks" The id for command blocks are 137
if you are on a server you will need to get permission from your administator. P.S i know you can use pressure plates
instead of command blocks! Also Make sure to subscribe to my channel for updated info! Link: www.youtube.com/dextersydney

(Hard Way, Manuel)

1. The first thing you will need is command blocks type /give (Your Name) 137
2. place the command block down now type testfor @p[x,y,z,r=5] you can change the number on the radius
3. now lets make a redstone clock place down 4 repeaters then put redstone to connect it.
4. link the redstone so that it will touch the command block
5. now were almost done you will need to place down a redstone detector to link the command block.
6. put a repeater after the redstone detector so it can send a better signal or whatever you call it.
7. now you can put any items (You must link the redstone dust) such as Redstone lamp, Pistons, Command blocks, dispencers, powered rails, redstone torches and etc.
8 Enjoy!


(Easy Way, Video)