Obviously since the part is commercially available, the bomb was fake. The Big Dog solves another one.
I admit I was getting a little suspicious myself, after a trip to Lowe's today in which I noticed whole shelves full of PVC pipe for sale.
As much as I hate to say it....
The clock Dog linked to is just a clock. It has no alarm. It is not clear to me how it could be used as a detonator.
That said, I'm not a clock-maker, nor an electrician, nor a bomb-maker. The only physical objects of any worth than I can make from scratch are bunny cages, children's play tables and such.
That said another that said, it may have some value as a detonator to someone more skilled than I. The guts of the little clocks may be made from very cheap mass produced digital watches or something, with some controls accessible inside the case. Imagine a the guts of a cheap wristwatch attached to a larger screen. Something like that.
If they did go off, they could do harm. People lose fingers and eyes to fireworks all the time. It's not hard to imagine some poor mailroom clerk losing an eye or some fingers, or getting an unlucky hit to the neck. Small doesn't mean harmless, it just makes it more personal.
They could be fake, in the sense that they didn't have full detonators. Or, the timer may have been backup for a physical trigger that didn't work. In one image, the clock face appears damaged. Who knows? It may take a few days (or much longer) for the details to leak out.
There are still a million things possible based on the little information that has been released. Maybe the bomber made a prototype, took it out in the woods, and it went "boom", but more due to luck than skill, so the subsequent bombs didn't go off because the original design was crap. Maybe they were all damaged in transit. Maybe between prototype and final batteries ran too low to actually make a spark.
Maybe, maybe, maybe.
Too soon to declare that they were not intended to detonate, but too soon to rule that out either.