The MS-2000 (M) distress marker light has come a long way since you purchased ACR's original Firefly back in the 1960s.
Here are a few of the new features found in all of our MS-2000(M) models:

• Shield extends/retracts for omni- or uni-directional visibility
• Waterproof down to 50ft (15.3m);
• IR filter blocks all visiblelight (lets through only IR light)
• Raised polarity indicators allow correct battery replacement in low or no visibility conditions
• New braided steel retainer keeps battery door from being lost
• Operates on 2 standard alkaline AA batteries - disposal causes no environmental impact
• For extreme cold environments or long term storage, use 2 common lithium batteries
• Blue filter distinguishes strobe from ground fire when in place

Specifications

Product Number: 3990 MS-2000(M)T

• Size: 4.5 x 2.2 x 1.1 in (11.4 x 5.6 x 3.3 cm)
• Weight: 4.0 oz (115 g) without batteries
• Light Output: 250,000 peak lumens per flash
• Flash Rate: 50 ñ 10 per minute
• Light Dispersion: White-omnidirectional, IR-omnidirectional, Blue-unidirectional
• Operating Life: 8 hours minimum-strobe; 2 hours minimum-incandescent
• Visibility: Military tested at a distance of 6 miles (9.6km) on a clear dark night
• Waterproof: To a depth of 50ft (15.3m); 200ft (61m) diver version available
• Batteries: 2 AA alkaline or lithium batteries (not included)
• Case Color: Black with olive drab flashguard
• Construction: Case, lens and flashguard-high impact polycarbonate; IR filter-butyrate
• Activation: Spark proof magnetic reed switch
• Limited Warranty: 1 year
• Federal Stock Number (FSN): 3990 only: 6230-01-411-8535