That really depends on the display mode chosen.
All methods can display a lot of text for an alert. The most limited mode is "Full Screen".
As you can see in the image above, the "Full Screen" display mode for ODA can display about 360 characters of text.
"Pop-ups" and "Scrolling" display messages can accept many more characters.
However, much like SMS, we recommend keeping Desktop Alert messages as short as possible.
In most cases, your end-users will dismiss a pop-up or scrolling bar quickly, so shorter messages will actually be read as opposed to ignored!