Despite limited efficacy data, do-it-yourself (DIY) insecticide products often promise low-cost alternatives to professional pest control. Total release foggers (TRFs, ‘bug bombs’), which are prominent DIY products, were recently shown to be ineffective at reducing German cockroach ( Blattella germanica L.) infestations, in contrast to highly effective baits. However, the reason(s) for TRF failure remain unknown. Therefore, we investigated insecticide resistance of apartment-collected cockroaches from homes where TRFs failed. In topical (direct) application assays, resistance to cypermethrin (a common active ingredient in TRFs) was 202 ± 33 times that of a laboratory insecticide-susceptible population (based on LD 50 ratios), while resistance to fipronil, a common bait active ingredient, was considerably lower at 14 ± 2 times that of the laboratory insecticide-susceptible population. The addition of PBO, a P450 inhibitor that synergizes pyrethroids, enhanced the efficacy of cypermethrin, but only at high doses of cypermethrin. Additionally, >96% of screened cockroaches possessed at least one copy of the L993F mutation in the voltage-gated sodium channel, known to confer resistance to pyrethroids (knockdown resistance, kdr). Because TRF treatments killed insecticide-susceptible sentinel cockroaches but failed to kill apartment-collected cockroaches, these results suggest that pyrethroid resistance is a major factor contributing to the failure of TRFs. Multiple mechanisms of resistance, including metabolic detoxification of the pyrethroids and kdr mutations that confer target-site insensitivity, suggest that TRFs would lack efficacy against German cockroaches in residential settings, where high levels of pyrethroid resistance have been documented globally.