A method of sensing a flow in a flow channel, the method comprising: performing a measurement cycle for a first period of time, wherein performing the measurement cycle comprises: supplying a current to a flow sensor (110, 200, 300), wherein the flow sensor comprises two upstream resistive elements (RU1, RU2) in the flow channel and two downstream resistive elements (RD1, RD2) in the flow channel arranged in a bridge, wherein the current is pulsed to the flow sensor; whilst current is being supplied to the flow sensor, resistively heating at least one upstream resistive element of the two upstream resistive elements (RU1, RU2) and at least one downstream resistive element of the two downstream resistive elements (RD1, RD2) to a temperature above an ambient temperature in response to supplying the current to the sensor, wherein when no flow is present the at least one upstream resistive element and the at least one downstream resistive element are heated substantially evenly so that the bridge remains substantially in balance; detecting an imbalance in the bridge resulting from a temperature difference between the at least one upstream resistive element and the at least one downstream resistive element in response to the flow of a fluid past the flow sensor, wherein the imbalance is related to a rate of the fluid flow past the flow sensor; powering off the at least one upstream resistive element and the at least one downstream resistive element for a second period of time, wherein no current flows to the at least one upstream resistive element and the at least one downstream resistive element during the second period of time; and performing the measurement cycle for a third period of time. performing a measurement cycle for a first period of time, wherein performing the measurement cycle comprises: supplying a current to a flow sensor (110, 200, 300), wherein the flow sensor comprises two upstream resistive elements (RU1, RU2) in the flow channel and two downstream resistive elements (RD1, RD2) in the flow channel arranged in a bridge, wherein the current is pulsed to the flow sensor; whilst current is being supplied to the flow sensor, resistively heating at least one upstream resistive element of the two upstream resistive elements (RU1, RU2) and at least one downstream resistive element of the two downstream resistive elements (RD1, RD2) to a temperature above an ambient temperature in response to supplying the current to the sensor, wherein when no flow is present the at least one upstream resistive element and the at least one downstream resistive element are heated substantially evenly so that the bridge remains substantially in balance; detecting an imbalance in the bridge resulting from a temperature difference between the at least one upstream resistive element and the at least one downstream resistive element in response to the flow of a fluid past the flow sensor, wherein the imbalance is related to a rate of the fluid flow past the flow sensor; supplying a current to a flow sensor (110, 200, 300), wherein the flow sensor comprises two upstream resistive elements (RU1, RU2) in the flow channel and two downstream resistive elements (RD1, RD2) in the flow channel arranged in a bridge, wherein the current is pulsed to the flow sensor; whilst current is being supplied to the flow sensor, resistively heating at least one upstream resistive element of the two upstream resistive elements (RU1, RU2) and at least one downstream resistive element of the two downstream resistive elements (RD1, RD2) to a temperature above an ambient temperature in response to supplying the current to the sensor, wherein when no flow is present the at least one upstream resistive element and the at least one downstream resistive element are heated substantially evenly so that the bridge remains substantially in balance; detecting an imbalance in the bridge resulting from a temperature difference between the at least one upstream resistive element and the at least one downstream resistive element in response to the flow of a fluid past the flow sensor, wherein the imbalance is related to a rate of the fluid flow past the flow sensor; powering off the at least one upstream resistive element and the at least one downstream resistive element for a second period of time, wherein no current flows to the at least one upstream resistive element and the at least one downstream resistive element during the second period of time; and performing the measurement cycle for a third period of time.