I thought I replied about this already but I don't see my response here so here I go again.
There are lots of ways they can find you.
Your neighbors may be video taping your front door and counting days you go through it and reporting this information to the OSTR.
They also can scrape the web and get information just like airdna has.
If they see your calendar has open nights and then they become unavailable, they may assume it's a booking and not that you "took it off the market" that night.
If this doesn't match up with your quarterly filing, this may trigger an audit.
As I understand it, currently it's almost all complaint driven, but they are collecting various bits of data.
They're also in talks with AirBnB to provide data .. if airbnb decides to provide data then it'll make it much easier for the city to catch you.
In cases like these, the burden of proof is always on the accused.. if the city thinks you're doing something wrong, you'll have to prove to them you aren't.
The quarterly reports are filed under penalty of perjury ... are you willing to risk jail time in hopes you don't get caught lying on those forms?
My advice is for people to host within the bounds of the law and report accurately your hosted and unhosted nights.
The consequences could be quite high.
Keith