There are several types of smart pens available in the global market. The most recent ones may be called a ballpoint pen type of personal computer. Despite of the highly advanced functionalities, however, none of the smart pens has capability to sense and record pen pressure data with itself.
DP-1000 electric pen developed and supplied by Japan System Development (JSD) has the capability to sense and digitized the data, so that the pen pressure data will be easily recognized and analyzed by computer when it is used for writing or drawing something on a paper sheet. According to JSD's web-site, proprietary and patented technologies are used for DP-1000.
My curiosity is, if the pen pressure sensing technology is built into a smart pen, the integrated product may perhaps create various applications which will be more than the deveopers' expectation. I hope I'll see it sometimes in the future.