Electronic – arduino – how to detect power failure and make micro-controller save data in EEPROM

Two things come to my mind:

First, according to the data sheet, a erase-write-cycle takes at least 0.8ms, and up to 2.6ms. You say that you have an interrupt every 1ms, which may lead to a write operation. I have seen in the code that you disable interrupts for parts of the erase and for parts of the write function. But you still might get funny interleaving of the function calls. Maybe it helps when you disable interrupts for the whole sequence of erase and write?

Second - you might want to write while to power goes down, and the EEPROM write happens exactly in the moment when the supply voltage goes below the operating voltage. You can try to monitor the supply voltage, and refuse a write when it is below, lets say, 4.5V. This assumes that it stays long enough above 2.7V as the minimal operating voltage, and brown-out-detection is set to trigger only below that point.

If memory serves, one-wire devices define a reset pulse is any low pulse longer than a specified duration (I think about 600us) with no maximum duration. Being unplugged for four months and then having voltage applied would qualify as a 10,368,000,000us low pulse, which is certainly longer than 600us. Consequently, the devices generally assert a "presence" pulse shortly after power is first applied. Depending upon contact bounce, it is possible that touching a device may not cause a clean reset, in which case one might possibly not get the "present" pulse, but I've found that triggering on a falling edge triggered by a remote device seems to be pretty reliable.