Following the more-is-better philosophy, the Bosch GPL5 uses five beams to project plumb, level, and square points. It also self-levels (up to 5°). Available for around $200, the 1 lb. unit is 4.125″ × 3.125″ × 1.625″, and can be secured using its 1/4-40 or 5/8-11 threaded mounts, or via straps or magnets with its multipurpose attachment. It can be easily re-calibrated in the field (and comes with a wrench for just that purpose). Its accuracy is ± ¼” @ 100′. Three AA batteries supply power.
If you’re not into multi-axis laser leveling, maybe you could modify the GPL5 for use as a garage/shop intruder alarm.