A method of pairing a therapeutic product delivery device to a handset is described. The handset is restricted to controlling only delivery devices which it is paired with. The method comprises the steps of: at the delivery device, setting, in response to the delivery device being connected to a charging device, a pairing indicator indicating that the delivery device is available for pairing, and broadcasting the pairing indicator using a radio transceiver; at the handset, discovering the delivery device based on the broadcast pairing indicator; and pairing the discovered delivery device and the handset together. By limiting the handset to pairing with devices which are broadcasting a pairing indicator, and by limiting the setting and/or broadcast of the pairing indicator to when the delivery device is connected to a charging device, the risk of accidentally pairing the wrong delivery device (for example someone else's) to the handset is greatly reduced.