Are electronic organizers popular in the 90’s secure?

In the 90’s electronic organizers like the Casio BN 20 were popular. They store phone numbers, calendar, and they have a secret section where data is protected by a pin. Of course, fast forward to today, our mobile phones can do much much more than any of these devices. Thus have rendered them relatively obsolete. However, my interest in these devices are that they are mostly offline devices. No internet or telephony.

My question, how safe are these devices in …

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