FMM-101 is a miniature monitor module (a mere 1.3" (3.302 cm) H x 2.75" (6.985 cm) W x 0.5" (1.270 cm) D) used to supervise a Class B (Style B) circuit of dry-contact input devices.
The L-PCM06B is also an excellent choice for multiple applications. It features a cone design, metal grille appearance plus a metal dome for great performance even in challenging environments.