Tony, My SeaRey has the ACI 2070B SeaRey Gear Alert--I think that's the formal name. It was developed by the Ontario SeaRey dealer, John Dunlop (ex-RCAF fighter pilot and Air Canada captain, ret, and builder of two SeaReys). I was a beta-tester--but that doesn't exactly indicate bias, because I had already flight-tested three other landing gear alerts, all for seaplanes, and rejected them. This baby is the best, probably on the planet.
It monitors landing gear position, flap position, and airspeed--as you'd expect. When it detects landing-position flaps and/or (used-set) approach-airspeed, it flashes two lights alternately and a strident woman's voice says in the intercom, "Select landing." That is,
it interrogates you, the pilot, about your intention. You then have to press the flashing light corresponding to "RUNWAY" or "WATER." If you press the correct one for the current landing gear position (up or down), the woman's voice says, "Water landing--okay" OR a man's voice says, "Runway landing--okay.
If you press the wrong light for the gear position OR if there's a landing gear asymmetry (one up, one down) or not completely locked, the strident woman says, "CHECK LANDING GEAR, CHECK LANDING GEAR..." over and over until you either press the correct flashing light or relocate the gear. It's very alarming when that happens, and I've never heard of anyone going past that point without recognizing that there's a landing gear problem. (You CAN ignore it, but not by accident!)
But the best feature of the ACI 2070B SeaRey Gear Alert is that after every takeoff it waits for about 50 seconds and then checks the gear position. If you've left the wheels down, is says, "RAISE GEAR. RAISE GEAR" to remind you that in an amphibian the wheels must always be up EXCEPT for a land runway landing. That's the best feature of all. (Especially in a SeaRey, which, being a high-wing pusher, can land gear-up on any surface and still fly away. (It might not float if the surface is coarse concrete, but it will fly.) I wouldn't buy the Alert until they added that feature. Recent versions repeat the warning later if you still haven't raised the gear.
All of those alert conditions can be disarmed temporarily--during stall practice, for example, or slow flight.
It's sold by ACI (Aircraft Components Inc, which also makes a somewhat less talented version for certified airplanes) and others, but here's the developer's ad for it, with probably the best price anywhere:
http://www.seareycanada.com/Specials.htm