This paper analyses the security and privacy properties of a widely used insulin pump and its peripherals. We eavesdrop the wireless channel using Commercial Off-The-Shelf (COTS) software-based radios to intercept the messages sent between these devices; fully reverse-engineer the wireless communication protocol using a black-box approach; and document the message format and the protocol state-machine in use. The upshot is that no standard cryptographic mechanisms are applied and hence the system is shown to be completely vulnerable to replay and message injection attacks. Furthermore, sensitive patient health-related information is sent unencrypted over the wireless channel. Motivated by the results of our attacks, we study the feasibility of applying cryptography to protect the data transmitted over the air and prevent unauthorized access to the insulin pump. We present a solution based on AES in combination with an updated message format optimized for energy consumption. We implement our solution on a 16-bit micro-controller and evaluate its security properties and energy requirements. Finally, we discuss potential strategies for further reducing the energy consumption.