Not the most exciting product but if, like me, you've been plagued with mice and conventional solutions are both unpleasant and fail to solve the problem this must be worth a try while it's half price. Mouse damage has cost me far more than this as well as the unpleasant health risks. For rats and cockroaches too.
There are various 'sonic' gadgets around but this one is simply plugged into any socket in the house and claims to provide an 'invisible force field' throughout the house via the mains wiring. If it works it will be well worth the £9.99 currently being charged in Tesco (was £19.99). Possibly reduced because it's out of season (problems are usually in winter).
Safe for children, dogs and cats.
The fact that Tesco are selling it gives me a little bit of confidence that it isn't 'snake oil'.