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Among the flaws in your reasoning, EMP energy is not concentrated in the 2.4 GHz range where microwave ovens and Bluetooth devices operate. The majority of the pulse energy resides in the frequency spectrum of 10MHz-100MHz which is the most predominant operating range for most electronic equipment. Microwave ovens direct the energy away from the front door which has less effective shielding in the form of a mesh that only provides 20-30dB of attenuation because people want to see what’s cooking. As long as the radios in your phone-watch system could overcome this amount of loss they will still work. The oven door reduced the signal by some amount just as increasing the distance between the devices would, but that doesn’t mean that it could not provide sufficient shielding effectiveness against an EMP pulse where most of the energy is at a much lower frequency. You may have noticed that AM radio tends to still work when you drive into a short tunnel whereas FM nearly always is lost immediately. That’s because the effectiveness of electromagnetic shielding of the concrete, steel, dirt, etc in the tunnel increases with frequency and FM operates at 100 times the frequeny of AM radio. Microwave ovens, Bluetooth, Wi-Fi and other devices operate at 2400 times the frequency of AM radio and share the Industrial Scientific and Medical frequency allocation there. Both Bluetooth and Wi-Fi use spread spectrum technology to skip over frequencies that are in use by other devices which is how they are able to work as well as they do.

I’m just sharing information, and I only mentioned the microwave oven as a readily available Faraday cage that is considered to be effective for the EMP spectrum. In fact, a portable device like a phone or tablet isn’t very likely to suffer any damage unless it’s plugged in at the time of an EMP.

Some may be interested in this summary and overview of EMP which is not too technical:

https://www.chds.us/ed/resources/uploads/2010/05/2017_HS_Summit_Lane_Electromagnetic_Pulses.pdf