Hydrazine (N2H4) is a toxic compound widely used in agricultural, chemical, pharmaceutical, and other industrial processes. It causes serious pollution to air, soil, and water. Therefore, the detection of N2H4 is one of the prime scientific interests. In this study, two novel reaction-based ratiometric fluorescence probes (Phe-HBT and Me-HBT) for the selective and sensitive detection of N2H4 are reported. The present approach, including the cyclization reaction induced by N2H4, enables to visualization of N2H4 at low levels by naked eyes under daylight or UV light with a fast response time of about 8.0 min for Phe-HBT and 16.0 min for Me-HBT. The detection limits of the probes were calculated to be 80.6 nM for Phe-HBT and 99.2 nM for Me-HBT. Both the probes displayed high specificities for N2H4 among the tested potential competing analytes. Both probes were applied to detect aqueous trace N2H4 in various samples such as food, soil, sewage water and living cells. Moreover, the detection of N2H4 was successfully tested by smartphone application as well as the detection of gaseous N2H4 by the modified fabric, showing its potential value in practical applications.