There is provided an apparatus that determines the location of an impermissible movement on a predetermined magnetically attractive object. Embodiments of the invention provide an electrically-pumped VCSEL having a number of different p-i-n junction and electrode arrangements, which, in various embodiments, allow independent biasing of the multiple active regions, and, in other embodiments, allow simplified electrical connections. In another embodiment, further power conservation may be afforded through a radio-triggered wake-up mechanism.