Steam Price Tracker sends you emails when the prices of the games you specify change in the Steam store.

Using Steam Price Tracker is easy. All you need to do is register a valid email address, if you haven't already, then log in, and start tracking apps (games).

Steam Price Tracker doesn't just track the price of the individual app or game, but every package of which the app is a part. That way, you'll know when the game your tracking is part of a good deal.

Whenever you track the price of a specific game or product, the Steam Price Tracker also tracks the price of every package it's in. So, for example, as long as you're tracking the price of Sid Meier's Civilization® IV, you'll get an email if the price of Package: Sid Meier's Civilization® IV: The Complete Edition changes. If you go to your Tracked Apps (while logged in) you may see that some of the listed games (like Civ 4) have multiple prices listed--the additional prices are the prices of the packages that they're in. And don't worry. You'll also be emailed if the game you're tracking is removed from or added to any package.

You're probably trying to track a package rather than an app. See How do I track packages?