Getting too close alarm on robot

[airman00]

I've been building this big robot(4 feet tall) for a display and one feature I have to add is a "do not touch me warning." Basically whenever a person gets too close to the robot with his hand or body or whatever, the robot must say "Please back up and do not touch me"

Any idea how to do that?

I was thinking of putting IR heat sensors in several places and detect people that way. I dont think I can do sonar because sonar does not have a wide enough beam angle, and I don't want to put 50 ultrasonic sensors

[Trumpkin]

I can't remember what It's called but this one guy at a robotics club I go to had a metal frame and when you got really close to it it sensed it. I'll try to find out more about it.  
*EDIT*
I think the metal frame must have been acting as a capacitive sensor.

[SmAsH]

I can't remember what It's called but this one guy at a robotics club I go to had a metal frame and when you got really close to it it sensed it. I'll try to find out more about it. 

would that use EMR?
I think ir would be one of the best approaches for this, how far are we talking?

[Razor Concepts]

Capacitive touch would be a good idea... a QT100A costs like a buck, turn up the gain really high and then it should work (as long as there is metal where you want the detection)

[spizzak]

I'm not sure how they work but I know a lot of motorcycle alarms have proximity sensors of some sort and they usually aren't too too expensive. Maybe if you find out how they work you can replicate that.

[HyperNerd]

I agree that capacitive sensing is a good idea. I saw somewhere on YouTube (can't find it now ) someone who added vibrating motors and a capacitive sensor to an old computer mouse, so when your hand got near it, it jiggled away.

Can't remember many details though

 -HyperNerd