The present invention relates to a device for monitoring integral value of time, temperature comprising at least one layer of polymer comprising a latent pigment capable of undergoing at least one colour change, and an organic acid or comprising one layer of polymer comprising a latent pigment capable of undergoing at least one colour change, and one layer of polymer comprising an organic acid, wherein said latent pigment is converted to its pigmentary form which causes said colour change. The device can be used for monitoring sterilization of medical and kitchen supplies, canned foods and doneness of microwave foods.
