US D423672 S
FIG. 1 is a front perspective view of a biofeedback sensor, showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a top plan view thereof; and,
FIG. 4 is a rear elevational view thereof.
The left and right side views of the system, as well as the bottom view of the system, form no part of the claimed design.