I have a 3 pin sensor.
How do I sense this with an arduino uno?
-which pins are needed
The receivers typically have +5V, GND and signal out (check the pinout as it varies for different models from the same suppliers)
In theory, you just need to connect the signal out to an interrupt pin on the Arduino (2 or 3 = INT0 or INT1 on Atmega328x Arduinos) and you should get a standard square wave
1kHz signal if you write the appropriate coded & Interrupt handler. If you are not comfortable with Interrupts you should be able to poll any pin - at that frequency(500Hz).
Just noticed 1ms on & 1ms off = 500Hz not 1kHz.
Caveat: some IR receivers cannot handle a continuous signal and turn off. You need to check the data sheet for your IR receiver.
Either of these should work fine: TSSP4038 TSSP58038 from Vishay (they run at 5V or 3.3V)