A hearing assistance system comprising a portable hearing assistance device comprising • an input unit for providing an electric input signal comprising an audio signal, • an output unit for providing on output signal originating from the audio signal, • a forward path between the input unit and the output unit, • an energy source for energizing components of the hearing assistance device, the hearing assistance device (HA; HI) further comprising • a control unit (DET-CTR) configured to control the activation of a low-power mode of operation of the hearing assistance device, wherein - when said low-power mode is activated - the draw of current from said energy source is reduced compared to a normal mode of operation of the device, the activation being decided based on a combination of at least two different control input signals (ID1, ID2, ID3, ID4) to the control unit (DET-CTR), each control input signal being a signal selected from the group of signals comprising ∘ 1) signals relating to a current physical environment of the hearing assistance device, ∘ 2) signals relating to a current acoustic environment of the hearing assistance device, ∘ 3) signals relating to a current state of a wearer of the hearing assistance device, and ∘ 4) signals relating to a current mode of operation of the hearing assistance device and/or of another device in communication with the hearing assistance device, wherein the portable hearing assistance device (HA; HI) comprises two or more detectors (DET1, DET2, DET3, DET4) configured to provide the at least two different control input signals (ID1, ID2, ID3, ID4) to the control unit (DET-CTR), and an auxiliary device, the system being adapted to establish a communication link between the hearing assistance device and the auxiliary device to provide that information signals can be exchanged between or forwarded from one to the other, and characterized in that the auxiliary device comprises a user interface adapted to allow a user to add a particular external detector to provide a further control input signal to the control unit, wherein the activation of the low-power mode is based on the combination of the control input signals. • an input unit for providing an electric input signal comprising an audio signal, • an output unit for providing on output signal originating from the audio signal, • a forward path between the input unit and the output unit, • an energy source for energizing components of the hearing assistance device, the hearing assistance device (HA; HI) further comprising • a control unit (DET-CTR) configured to control the activation of a low-power mode of operation of the hearing assistance device, wherein - when said low-power mode is activated - the draw of current from said energy source is reduced compared to a normal mode of operation of the device, the activation being decided based on a combination of at least two different control input signals (ID1, ID2, ID3, ID4) to the control unit (DET-CTR), each control input signal being a signal selected from the group of signals comprising ∘ 1) signals relating to a current physical environment of the hearing assistance device, ∘ 2) signals relating to a current acoustic environment of the hearing assistance device, ∘ 3) signals relating to a current state of a wearer of the hearing assistance device, and ∘ 4) signals relating to a current mode of operation of the hearing assistance device and/or of another device in communication with the hearing assistance device, wherein the portable hearing assistance device (HA; HI) comprises two or more detectors (DET1, DET2, DET3, DET4) configured to provide the at least two different control input signals (ID1, ID2, ID3, ID4) to the control unit (DET-CTR), and an auxiliary device, the system being adapted to establish a communication link between the hearing assistance device and the auxiliary device to provide that information signals can be exchanged between or forwarded from one to the other, and characterized in that the auxiliary device comprises a user interface adapted to allow a user to add a particular external detector to provide a further control input signal to the control unit, wherein the activation of the low-power mode is based on the combination of the control input signals. ∘ 1) signals relating to a current physical environment of the hearing assistance device, ∘ 2) signals relating to a current acoustic environment of the hearing assistance device, ∘ 3) signals relating to a current state of a wearer of the hearing assistance device, and ∘ 4) signals relating to a current mode of operation of the hearing assistance device and/or of another device in communication with the hearing assistance device,