Has anyone ever used one? Going on holiday next week with 4 kids (10, 7, 5 and 3) to a villa which has a pool with no fence or alarm so about to splash out £75 for a portable alarm where the child wears a wrist band and the base unit sounds when the band in submerged in water. The 3 year old can swim one or two strokes but is definitely not a strong swimmer. We will obviously put him in arm bands but wondering in the alarm will help or if it will be one of those things that isn't used and therefore a waste of money. Has anyone used one?