Devices, systems and methods are disclosed that allow a patient to self-treat a medical condition, such as migraine headache, by electrical non-invasive stimulation of a nerve, such as the vagus nerve. A stimulator comprises a contact surface for contacting an outer skin surface of a patient and a pulse generator coupled to the contact surface. The pulse generator is configured for attachment and electrical coupling to a mobile device configured to receive a wireless signal, such as a mobile phone. The pulse generator is further configured to generate an electrical impulse and to transmit the electrical impulse through the contact surface and the outer skin surface of the patient to modulate a nerve within the patient.