Safe assets are a cornerstone of the modern international financial system. I show the existence of a time-series dimension of safety: the perceived safety of an asset can oscillate over time, with relevant real implications. I construct a text-based index from newspaper mentions, the FLY, to measure global demand for safe assets and flight-to-safety episodes, and I estimate time-varying loadings on the index for a large dataset of sovereign bonds of all maturities from both advanced and emerging economies. I identify switches in a bond's safety through changes in the sign and statistical significance of its loading on the FLY. Safety switches are not uncommon, both in advanced and in emerging economies, they happen across credit rating classes, and are not fully captured by changes in ratings. Safety switches also have important real implications: while a positive switch (i.e. becoming safe) is not expansionary, a negative switch (i.e. becoming risky) depresses output by up to 0.7 percent for a year. Investment and government spending are particularly affected, falling by as much as 3 and 2 percent, respectively, in the first two years after the switch. Positive safety switches also lead to an increase in debt, as countries take advantage of their newly-gained safe status, while negative switches lead to a decrease in debt and a persistent shortening of its maturity structure, with long-term debt to GDP falling by 6 percentage points in the five years following the switch.