Help with alarm project

I am trying to help build a very small flat portable alarm. Maybe the size of half a credit card and 3x thickness for a daughters project

I wanted to start with a 3V2016 Lithium Battery 10A19. Can someone help me with
a flat low profile transformer that I could use to step the volage up maybe 5X. Also if you had a schematic I would be very grateful.

Thanks for helping..

A transformer works with AC voltages. You can't step up the DC voltage of the battery with one directly: you must first chop the voltage on and off, to give a 'pseudo AC' voltage, as is done in switch-mode power supplies (SMPS). Producing an SMPS only 3 x credit-card thickness is a tough challenge and maybe beyond the capability of a hobbyist. Even obtaining a small enough inductor and capacitors may prove tricky. If you found some way of deriving 15V, how much current are you hoping to draw (which would help us to determine if the project is feasible)?

alec_t - thanks for the reply. I would like to create a 110dB sound. I believe that I can get a paper thin inverter. I am not sure of what the current needs are.

Personal alarms small enough to hang on a key-ring are sold cheaply. Easier (and probably cheaper) than making your own.