Comparison between the outer orbital period of a triple system and the factor on the right-hand side of Eq. (9). Red points represent T_lim vs. the outer orbital period T₂ for all the Galactic LISA double white dwarfs with a bound third star. The black line represents the points where T₂ = T_lim. No tertiary star satisfies Eq. (9) for detectability within the LISA frequency bandwidth.