Temporarily provisioning functionality to a personal device in a multi-device point-of-sale (POS) system is described. In an example, a personal device can be determined to be within a range of a POS system of a merchant. The POS system can include a merchant-facing device and a customer-facing device that is coupled to the merchant-facing device. Functionality can be provisioned to the personal device that (i) configures the personal device to present a customer user interface (UI) via a display of the personal device to enable a customer operating the personal device to interact with the merchant and (ii) enables the personal device to interact with at least one of the merchant-facing device or the customer-facing device. Responsive to determining an occurrence of an event, the functionality can be de-provisioned from the personal device.