integer mode;

default
{
    state_entry()
    {

    }

    touch_start(integer total_number)
    {
        mode = !mode;
        if (mode) {
            llParticleSystem([put here your particle system]);
            llOwnerSay("Particles enabled");
        } else {
            llParticleSystem([]);
            llOwnerSay("Particles off");
        }
    }
}