The ornamental design for a controlpanel for a security system, as shown and described.
FIG. 1 is a perspective view of a control panel for a security system;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a back elevation view thereof;
FIG. 4 is a top elevation view thereof;
FIG. 5 is a bottom elevation view thereof;
FIGS. 6-7 are side elevation views thereof; and,
FIG. 8 is a back perspective view thereof.
The broken line showing of various elements in the drawings are included for the purpose of illustrating portions of the “article” and form no part of the claimed design.