One's a timer, and the other is a Hex inverting Schmitt trigger - which you use depends what you're trying to do, there are a great many different ways to make a simple alarm circuit.
If you want a very simple alarm sound that is a continuous steady tone then use a 555.
But the 6 Schmitt Trigger inverters in a 74C14 or 74HC14 can make 6 different frequencies. One frequency can be changed slowly by one of the other slower frequencies with a diode or resistor, or the tone can be turned on and off and beeping with a diode gate.
You can do a *lot* more with a 7414 (or a CD40106) than you can with a 555, especialy if you have one handy, and you can drive a piezo sounder with it as well. Swings and roundabouts really.
I have never seen a CD40106 but I have used a CD74C14 and an MC14584 which are also ordinary Cmos hex Schmitt-trigger inverters. Their supply is from 3V to 18V. Each part has its own threshold voltages.