A series of luminescent iridium(III) complexes were designed and evaluated for their ability to detect oxalyl chloride ((COCl)(2)) at ambient temperature. In the presence of (COCl)(2), a double amidation reaction takes place at the diamino functionality of complex 1, leading to the switching-on of a long-lived red luminescence with a 9-fold enhanced emission. Complex 1 exhibited high sensitivity and selectivity, with a detection limit for (COCl)(2) at 32 nM. Additionally, complex 1 can be used to detect (COCl)(2) using a simple smartphone, allowing for the portable and real-time monitoring of (COCl)(2).