J SAINSBURY and its supermarket rivals are planning 'happy hour' trials, during which prices will be slashed at off-peak shopping hours. The concept will require new technology, enabling stores to change their prices at a key-stroke. This will be installed in the autumn, when a central database will enable prices on the shelves to be changed instantly via radio or infra-red signals. Apart from 'happy hour' themes, the technology allows supermarket managers to introduce a complex range of pricing strategies aimed at trumping local competition. [Debrief can also envisage dramatic promotional use of this development. Ultimately, bye-bye coupons?]