Watch a product
Read automatically (seen working): John Lewis, LG, Apple, Bose, Sonos, Scan, AWD-IT, and any shop that puts its price in the page's data (Dell, Lenovo, HP, Microsoft, Costco, Richer Sounds, Peter Tyson and Marks Electrical serve their pages; a product page is tried when you add it). Block automatic checks: Argos, Very, Littlewoods, Currys, AO, Amazon, CCL, Box, Laptops Direct, Appliances Direct, Reliant Direct, Novatech, PC Specialist, Chillblast, Sony, Dyson, Jessops, Smyths, and Samsung UK does not put its price in the page: those are watched by hand, you type the price in when you see it (the alert still fires). Any other shop is tried; if it refuses, it is marked blocked and switched to by-hand. "Normal" is what you type, or else the highest price seen in the last 90 days.
Deal watch: anything that drops far enough
Reads the deals HotUKDeals members post (its public RSS feeds: hot, newest and the tech tags), one feed a minute, every 3 hours. A deal counts when its price is the % off what the post says it was (RRP, was, usually…), or the post states the % off. Prices are as posted; check the shop before buying.