On your presentation, a timekeeper ting a bell.
However, it's difficult for him/her to keep the time on the fascinating presentation (or boring and causing drowsiness one).
Then, this app can keep time and ting a bell at predetermined times.
Of course, the bell also rings when you tap it.

･ Several types of bell/vibration are available.
･ This app can run in the background even with the screen off unless you finish this app by the back key or recent apps.
･ Low CPU use rate (0.02s when this app is running in the background on Nexus 5)