A wireless feedback device for monitoring an implant unit configured for location in a body of a subject is provided. The device may include a flexible substrate configured for removable attachment to the subject's skin, a primary antenna disposed on the flexible substrate, an interface configured to receive from the primary antenna a feedback signal based on wireless interaction with a secondary antenna associated with an implant unit configured to be located in the body of the subject, and at least one processing device. The at least one processing device may be configured detect a feedback signal on the primary antenna after cessation of a transmission to the secondary antenna, analyze the feedback signal to determine information relating to a function of the implant unit, and cause at least one response based on the analysis of the feedback signal.