Do "at the start of your turn" abilities work due to a swap with Alarm-o-Bot?

Let's suppose that, at the beginning of my turn, Alarm-o-Bot (previously played) is exchanged with a creature in my hand, having an "at the beginning of your turn..." ability. Does the latter ability take place? Or my turn is no longer considered to be "at the beginning"?

As an example, let's suppose that Alarm-o-Bot is exchanged with a Doomsayer. Are all the minions instantly destroied?

Thank you.