Asset market model: views currencies as an important asset class for constructing investment portfolios. Asset prices are influenced mostly by people's willingness to hold the existing quantities of assets, which in turn depends on their expectations on the future worth of these assets. The asset market model of exchange rate determination states that “the exchange rate between two currencies represents the price that just balances the relative supplies of, and demand for, assets denominated in those currencies.”
Traders who understand indicators such as Bollinger bands or MACD will be more than capable of setting up their own alerts. But for the time poor, a paid service might prove fruitful. You would of course, need enough time to actually place the trades, and you need to be confident in the supplier. It is unlikely that someone with a profitable signal strategy is willing to share it cheaply (or at all). Beware of any promises that seem too good to be true.
The need to exchange currencies is the primary reason why the forex market is the largest, most liquid financial market in the world. It dwarfs other markets in size, even the stock market, with an average traded value of around U.S. $2,000 billion per day. (The total volume changes all the time, but as of August 2012, the Bank for International Settlements (BIS) reported that the forex market traded in excess of U.S. $4.9 trillion per day.)