The ornamental design for a heatdetector, as shown and described.
FIG. 1 is a perspective view of the heat detector;
FIG. 2 is another perspective view of the heat detector of FIG. 1;
FIG. 3 is a bottom plan view of the heat detector of FIG. 1;
FIG. 4 is a left side elevation view of the heat detector illustrated according to the perspective view of FIG. 2;
FIG. 5 is a right side elevation view of the heat detector illustrated according to the perspective view of FIG. 2; and,
FIG. 6 is a top plan view of the heat detector of FIG. 1.
The broken line showing of a battery compartment, battery, and screw heads is included for the purpose of illustrating portions of the “article” and forms no part of the claimed design.