American border patrol already has significant surveillance powers and collects vast amounts of data on who is flying into and out of the country. But the U.S. has another tool to watch over travellers across the world thanks to a little-known but influential Texan business called Sabre. As the biggest of three companies that store the vast majority of the world’s travel information—from airline seats to hotel bookings — Sabre has been called on to hand over that travellers’ data and, on at least one occasion, do “real-time” tracking of a suspect. And, say former employees, the same powerful trove of information could be used to help monitor the spread of the Covid-19 pandemic.