An indicator alert is based on one of several technical studies.

Set up a forex indicator alert
Average Directional Index (ADX) / DMI
Bollinger Bands
Commodity Channel Index (CCI)
Elliot Wave Oscillator
MA Convergence-Divergence (MACD)
Moving Average (Simple)
Moving Average (Weighted)
MovingAverage (Exponential)
Parabolic SAR
Relative Strength Index (RSI)
Rate of Change (ROC)
Stochastics
Williams %R