Worried about over-spending this holiday season? If you’re the kind of person who easily gets sucked into all the sales – whether online or out in the real world – then this Proverbial Wallet just might be the solution to curbing your shopaholic ways. Designed by a team of researchers at the MIT Media Lab, these high-tech billfolds are digitally tied to your bank account levels, reacting to any fluctuations in your current balance by shrinking in size, refusing to open, or vibrating whenever a transaction is processed.