When you get an alert it means that someone or somewhat did create some kind of turnover in the Betfair Markets. As a basic rule you can interpret the alerts as follows.
A Turnover/Spike in the UNDER Markets on Betfair, means there was a Lay Bet, since based on the Mechanics of the Exchanges you only can Lay huge Amounts in a falling Market , you can’t back it. Hence we interpret this as a Lay bet.
The same is true for the Over Markets. You can ONLY Back huge Amounts in a rising Market. Hence it’s interpreted this as a Back Bet.
Concerning the strategy #5, you must know that the spikes are mainly used to bet on an almost certain imminent goal, not only on the final result. Spikey users usually mainly LAY the under and BACK it after a goal.
The screenshots below will show you some examples of good bets placed thanks to Spikey. Spikey offers there several possibilities, and you will learn them by using it: sometimes you will only LAY the current Under, sometimes you will prefer to place LAY bets on several markets (Under 2.5, Under 3.5 and sometimes The Draw in Match Odds market).