The ornamental design for an alarmhousing, as shown and described.
FIG. 1 is a perspective view of the alarm housing.
FIG. 2 is a front elevation view thereof.
FIG. 3 is a left side elevation view thereof.
FIG. 4 is a right side elevation view thereof.
FIG. 5 is a top plan view thereof; and,
FIG. 6 is a bottom plan view thereof.
The broken lines in FIGS. 1-6 depict subject matter that is hereby disclaimed and forms no part of the claimed design. The rear view of embodiments of the alarm housing illustrated in FIGS. 1-6 is intentionally omitted and do not comprise additional features of the claimed design.