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i don't have alot of experience with them but it seem to be exactly what i need.

i have a device that has a constant current of 3v as a continuity test that i can wirelessly get to momentarily jump to 9v for 3 seconds before dropping again. i would like to use it to hook up to the LEDs around my back yard so i can turn the lights off around the grill, gazebo or where ever the kids leave them on at. I believe if i understand correctly a thyristor is basically an electric switch, apply a certain amount of voltage once, it closes the circuit, lights on, do it again, opens the circuit, lights off. Do i understand this correctly and can i get a recommendation on which thyristor would work best?

If a thyrstor (SCR, silicon controlled rectifier) is controlling a dc circuit it will turn on when a voltage pulse is applied to the gate. Once turned on it will not turn off until the dc (not the gate) is turned off.

so that means that as as long as there is power going through the gate from the power source not the 9v source of the voltage pulse, it will stay on....

i have 2 terminals that can deliver the 9v pulse that stay at 3v constantly. what if i put a PNP transistor between the power source and the thyristor. If i deliver a pulse to it, it should cut the DC power to the thyristor, resetting it to be turned on again?

No No No A short voltage pulse on the gate turns the thyristor on and it stays on for evermore even after the gate pulse goes back to zero. The only way to turn it off is to remove the power source.

See the illustration circuit at https://www.circuitlab.com/circuit/6u2qfvqyfdd5/scr-illustration/