This invention relates to emergency flotation devices, particularly to a wearable device in the form of a collar; and most particularly to a device suitable for wear by a pet or young child which may be worn during watersports, and which will not deploy until predetermined nominal safety parameters have been exceeded. The present invention provides a personal flotation device, suitable for children, pets or the like, which will activate automatically in response to changes in pressure, e.g. water depth, time of submersion, or a combination thereof. As the device senses the change in pressure or time of prolonged submersion, the internal triggering mechanism punctures a hole permitting the compressed gas reservoir contained therein to be released, thereby inflating the device' s inner flotation member.