peak detection - Derivative calculation

I have a series of data (single array). If I take this data and plot it, I can see that there are multiple peaks. However If I zoom in to a section of data, I see that there is substantial noise.

I like to detect how many peaks in the data using little CPU time and energy. I thought of detecting the slopes of these peaks (could be sharp or smooth rising or falling) and look at the number of slopes to determine the number of peaks. (2 slopes positive and negative for every peak)

Any pointers how I can calculate the slopes in the presence of noise?

The code will go into an embedded system, memory is limited so preferably I like to implement something that doesn't require any significant data copy.