Empirical identification of the effects of monetary policy requires isolating exogenous shifts in the policy instrument that are distinct from the systematic response of the central bank to actual or foreseen changes in the economic outlook. Because the same tools are used to both induce changes in the economy, and to react to them, distinguishing between cause and effect is a far from trivial matter. One popular way is to use surprises in financial markets to proxy for the shock. In a recent paper, I argue that markets are not able to distinguish the shocks from the systematic component of policy if their forecasts do not align with those of the central bank. I then develop a new measure of monetary shocks, based on market surprises but free of anticipatory effects and unpredictable by past information.