The answer to your question, (surprisingly to me!) is YES. The two most common types of smoke detectors DO emit things (one uses light, one uses radiation).
Read all about them here: http://home.howstuffworks.com/smoke.htm
However, this is NOT A GOOD REASON to disable them! Your landlord, if this is his reasoning, is definitely lame in the brain. Most likely (because of cost), your smoke detectors are photovoltaic. They put out tiny bits of light. This is harmless. Even IF they are the ionization type, you'd have to break one open and stand in front of it for a thousand years to suffer any ill effects!
I'm exhaggerating, but you get the point. The fire codes should be followed, and the detectors should have batteries.
But hey, I learned something in looking this up! I would have bet money they were totally passive.