Comment by hollerith
Actually, I trust Apple's hardware security enough that I think it is probably impossible for anyone in China (even though they have physical access to the devices) to alter an iPhone or Macbook so that its own electronics can be used to trigger any explosive the attacker might install in the device, so in addition to an explosive, the attacker would need to install his own radio receiver. And the attacker probably won't be able to use the device's electronics to eavesdrop on the device's user, so no ability to tell whether the user is in the group the attacker wants to target unless again the attacker installs his own electronics (including radio transmitter) to do the eavesdropping.
An Iphone should weigh X grams. I think you should be able to detect tampering by weighing it.
I don't whats the margin of error/variance that passes quality control.