This letter introduces timing channels in connectionless Bluetooth low energy (BLE). The proposed standard-compliant enhancement, BLE with timing channels (BLE-TC), improves the energy efficiency of an energy-constrained connectionless BLE transmitter by encoding additional information in the interarrival time between BLE advertisements. BLE-TC is analytically compared with the connectionless BLE standard. Using realistic timing noise that is empirically determined through a proof-of-concept implementation, the results indicate that more than 10% improvement in energy efficiency can be achieved for low-throughput applications, such as smart metering and environmental sensing for smart cities.