Cell based sensor. The present invention relates to a novel cell based sensor useful for drug discovery that comprises a cell line with professional regulated exocytosis of secretory granules transfected with a non-protease hydrolase as a reporter polypeptide stored in the regulated secretory granules of the cell line with professional regulated exocytosis and having either an endogenous or a heterologous molecule as a modulator of regulated secretory granules exocytosis. Said granule stored non protease-hydrolase reporter having at least: a high resistance to conditions already present inside the granules such as low pH and proteolysis by other proteases; enzymatic activity after exocytosis; a highly specific substrate; absence of toxicity when cell thawing; a very low level of secretion under unstimulated or basal conditions; and a high signal to background activity in a media compatible with cell culture viability and granule exocytosis for a high throughput robust and sensitive detection.