There are four:

• One in the red area, probably the first one to get. From the save point near the hub, go through the door to the hall with 3 bots, then the door in the floor below guarded by the big bot, then the grate at the opposite end. You can't miss it after that.
  
• Second one is in yellow area, in the no-weapons zone, floor 2
  
• Third one is in the very top of the black (darkness) area
  
• A fourth one hidden in the very last save point of the blue area

You only need 2 to beat the game or 3 to get the useless card.

Originally posted by Darak:

There are four:

• One in the red area, probably the first one to get. From the save point near the hub, go through the door to the hall with 3 bots, then the door in the floor below guarded by the big bot, then the grate at the opposite end. You can't miss it after that.
  
• Second one is in yellow area, in the no-weapons zone, floor 2
  
• Third one is in the very top of the black (darkness) area
  
• A fourth one hidden in the very last save point of the blue area

You only need 2 to beat the game or 3 to get the useless card.

I did it took me to the place where I need a reciever I'm talking about red reciever

If you need more detailed instructions follow this walkthrough.

You can get the useless card with only two receivers, fyi. Just put both on one side of the door and then spam the other two buttons (and the clicker) and it'll open (source: too stupid to find more than two receivers).

the red one is the most difficult to get.
u have to fight a total of 6 robots, while the black one just 3.
and the yellow one just need some tricks on switching power to open the gate.

You don't have to fight the bots in red you just have to be quick or use mines. In black you only have to kill the Slashers though you might be able to run from them.