Some electronic locks have backdoors, like a manufacturer or master code. Once I was in a hotel and forgot the safe number, and someone entered the master code to open it. Would be interesting to see the assembly code of the chip.
There is a company who claims they can read the code of the ST62T25 (I assume that the read protection bit is set, or the OTP device can't be read at all usually). They don't write how expensive it is (but "low cost"), but I've heard that such services are expensive.
Regarding the power analysis: Dave, you are using 20 ms resolution. The chip is probably running at 8 MHz. You might not see the interesting things. If you measure it after the voltage regulator at the Vcc pin of the CPU on the control board, it might be possible to measure more high frequency signals (I would like to see how the chip whisperer works for this). Then you could try to build a selective amplifier for interesting frequencies to try to detect it at the battery contacts as well.