A wireless monitoring device, comprising: a housing (10) in which is contained a wireless communication circuit for sending and receiving wireless signals; first and second flexible band portions (12, 14) connected at respective first ends to opposing edges of said housing; at least one antenna coupled to said wireless communication circuit; a connection device (16) for connecting second ends of said first and second band portions (12, 14) together to form a flexible band configured to attach the device to a user; at least one magnet (22) positioned in said first band portion (12); and a magnetic field sensor positioned in said second band portion, wherein said magnetic field sensor (20) is arranged to detect said at least one magnet (22) when said band portions (12, 14) are connected together.