Trouble using a TSSP77038 with an Arduino
Gerben is correct it looks like you need a pull up resistor so that the pin is high unless the receiver drives it low.

I found this, which was the closest to useful information I found. Have a look at the proximity sensor section, it is similar to what you are using.

You'll want to know a value, I haven't got a clue.  I use 4.7K for I2C pull ups. It's probably easier to start high (weaker) and work your way down, because if you put a 100K resistor in and the signal is low, then the resistor is too strong and you need a smaller one.