my guess is that they're buying put options on the shiller home-price index, at a strike price 20% below the spot price.
though, those indices are only granular at the city level, whereas during a recession all neighborhoods in a city don't drop in value by the same rate - eg for bay area in 2008, east bay got decimated, whereas palo alto/peninsula barely dropped 5%.
though, those indices are only granular at the city level, whereas during a recession all neighborhoods in a city don't drop in value by the same rate - eg for bay area in 2008, east bay got decimated, whereas palo alto/peninsula barely dropped 5%.