Abstract: Devices useful to monitor whether or not an article has been exposed to sterilizing conditions are provided and comprise a package and an indicator associated with the package. The package is sufficiently permeable to admit sterilizing gas or vapor into the package. The indicator associated with the package changes color from a first color (indicating ambient conditions) to a second color (indicating exposure to acidic gas or vapor). Both the first and second colors of the indicator are stable and preferably substantially maintain their colors under ambient conditions. Particularly, preferred embodiments are adapted for use with peracetic acid sterilization processes.