Theory: A prismatic battery with an explosive core and an electronic fuse swapped to trigger the explosive instead of disconnect the battery. Firmware change to short the battery. No visible signs of tampering even in iFixit like conditions.
15g of explosives is sufficient, probably, based on the analysis I’ve seen.
15g of explosives is not very big.
The speaker is another potential home, that is a good point. Big cone and heavy magnetics.
This display weighs 15g, and uses cheap glass and old liquid crystal: https://www.crystalfontz.com/product/cfag12864u3nfhe11-128x6...
Would someone be able to make one that worked but weighed eg five grams, then fill the rest with explosive? Would anyone be able to discern that the back of the glass wasn’t liquid crystal but explosive, especially as they are usually taped over?
The best evidence we have now suggests that the devices used had removable (AAA) batteries, not built-in batteries.
If I was buying pagers and had previously been hit by intelligence ops I would be buying batteries in random supermarkets.