Another signal item we've started carrying in our lifejacket is a laser flare. It is waterproof to 80 feet and visible as a line of light for up to miles with optimal conditions mile away. The run time on the small one we carry is 40 hours continuous use. We did a product review in the August 2002 issue of Sea Kayaker and found they performed as advertised. They are a nice addition to your aerial flares, VHF, and SPOT. Back in my marine retail days we called those alert devices while smoke, a hand held flare or the laser flare would be the locate portion of the formula. It's important to be found once you've let someone know you are in trouble.

We once set out into the night after seeing flares go off in the distance. With nothing being used as a location signal we ended up searching for quite a while before locating the vessel in distress. Had the emergency been more severe the lost time could have been important, as it was we just had to tow the boat back to our anchorage and assist in some engine repair.

The laser flare is different than a laser pointer and is used by several organizations, including the military, as a means of signaling aircraft. The following comes from Greatland Laser's website FAQ section.

6. Won't they stun the pilot/captain whose attention I'm trying to get?

No. When the fan of light crosses your target's vision it will appear as a brilliant flash in the distance and will in no way impair their night vision.

Comparison of cockpit illumination power densities of Rescue Laser Flare®
emergency signaling device vs. typical laser pointer

Let’s compare the amount of laser light power which illuminates an aircraft cockpit from the Rescue Laser to that of a typical laser pointer, at a common signaling distance of 1.5 miles. The laser power level illuminating the cockpit and hitting the pilot’s eye from the Rescue Laser is about one trillionth of a watt. This power level is very low because the Rescue Laser begins with a very small amount of laser light and then creates a very long 2 dimensional fan (line) of light further reducing the power density of the light. This level can be easily detected, but will not obscure pilot vision in any way.

However, because the light from the laser pointer remains in a relatively small one-dimensional pencil thin beam, the laser beam spot size at the aircraft is about 240CM (8 ft) in diameter. Because all of this light is concentrated in a relatively small spot, rather than spread out in a long line like the Rescue Laser, the power density impinging on the pilot’s eye is about 1,000 times greater from the laser pointer, at this distance.

Therefore, although the signaling capability of the Rescue Laser emergency rescue and signaling device remains effective for signaling SAR aircraft, the power levels (brightness) of the Rescue Laser is reduced by one thousand times, this is a level where visual flight acuity is not affected.

It should be noted that even the laser pointer’s output although bright, is still about ten thousand times lower than the power level where eye injury can occur, at this distance.

A bit more from the military side Not part of the FAQ
The US Navy reported in a 2003 Aviation Survival Gear Field Test that "this signal laser is perhaps one of the best night signals invented." The Rescue Laser Light has been a popular addition to survival kits used by U.S. Army and Air Force personnel deployed in Iraq and Afghanistan.

The Joint Personnel Recovery Agency (JPRA) successfully tested Greatland Laser’s signaling devices in 2006. Results from a test of the Green Rescue Laser Flare® with the 12th Aviation Battalion at Fort A.P. Hill, Virginia found "an individual on the ground was able to successfully signal an aircraft flying at 2,000 feet out of five nautical miles during daylight to dusk condition." During Desert Rescue, the Green Rescue Laser Flare® was used to signal the rescue helicopter flying at approximately 50 – 200 feet out at two nautical miles in midday and full sun. The aircrew stated they were able to quickly pick up the bright flashes from the laser and vector in on the survivor.