The competitive strategies of `gatekeeper' platforms are subject to enhanced scrutiny. For instance, Apple and Google are being accused of charging excessive access fees to app providers and privileging their own apps. Some have argued that such allegations make no economic sense when the platform's business model is to sell devices. In this paper, we build a model in which a gatekeeper device-seller facing potentially saturated demand for its device has the incentive and the ability to exclude from the market third-party suppliers of a service that consumers buy via its devices. Foreclosure is more likely if demand growth for the platform's devices is slow or negative, and can harm consumers if the device-seller's services are inferior to those offered by the third parties.