A battery-powered environmental control and/or sensor device is disclosed. The device includes a mounting plate arranged to be affixed to a support surface; and a main body including a battery compartment. The main body is adapted to be releasably secured to the mounting plate, with the battery compartment being substantially inaccessible when the main body is secured to the mounting plate. The mounting plate and main body comprise complementary securing elements arranged to secure the main body to the mounting plate. The mounting plate or the main body include a lever having a portion extending beyond a periphery of the device so as to be operable by a device user when the main body is secured to the mounting plate. The lever is operable when activated to disengage the complementary securing elements and separate the main body from the mounting plate to provide access to the battery compartment.