MANY firms help businesses crunch data on their customers. Until recently, few have offered those services to the consumers themselves. Now a number of start-ups are offering "data lockers," secure online locations where people can gather information on themselves, including their consumption patterns - utility bills, loyalty-card statements, telephone records and so on. By helping them to retrieve those data in the first place, locker firms hope to give privacy-conscious consumers more control over what information organisations hold about them. They also aim to help people to reuse it for their own benefit. Consumers might give details of their past energy bills to price-comparison engines, to find them better deals. They could let retailers peek at their spending patterns in return for discounts. Shane Green of Personal, one such locker provider, thinks individuals who make full use of their personal data might one day earn $1,000 a year in benefits and savings. These firms, and the technology underpinning them, are young, and their business models unproven. Furthermore, consumers may regard their personal-data trail as something rather sinister that they would prefer to see erased, not an asset that is worth managing like cash in a bank. Mr Green hopes to win them over with some of his simple data-handling tools, such as one that automatically fills in consumers" personal details on web forms when they are shopping online. A bigger obstacle to widespread use of lockers is that they will thrive only if users can claw back personal data from the utilities, banks and shops that are collecting them. Britain's government may soon force some firms to give customers digital copies of information held about them; a proposed European Union law may enshrine similar rights across Europe. Elsewhere, data-locker firms will need to convince firms that they have more to gain from sharing data than hoarding them. Maarten Louman of Qiy, a Dutch foundation that promotes smarter use of personal data, argues that it may indeed be worth companies" while to do so. By helping consumers compile comprehensive profiles of their habits and preferences, they may in return be granted much richer data than they could collect without their customers" co-operation. Mr Louman says some large businesses already pay locker firms to deliver to their employees digital copies of their pay slips and pension statements. That saves the firms money, and keeps the locker service free to consumers. By making it easier for consumers to provide information, as well as receive it, personal lockers also could help companies keep their data up to date, says William Heath of Mydex, another locker provider. For instance, people moving house could simply update their address in their data locker, and then let their bank, utilities and other service providers retrieve it. There is a risk that if data lockers prove as useful as the start-ups claim, it could encourage bigger cloud-storage firms such as Google and Dropbox to barge in and grab their customers. Another danger is that locker users are tricked by disreputable companies or data thieves into exposing the masses of personal information in them, triggering a public backlash. In the longer run, insurers and other potential traders of personal data may require ever more intrusive volumes of information before giving price quotes. Indeed, if the trading of personal consumption data becomes common, a time may come when shoppers will have to reveal all about themselves or be charged top whack for everything they buy.