Isn't it risky to sell old smartphones and PCS ?

[hawker9000]

If you want peace of mind, take the laptop to a computer shop have the hard drive replaced and a fresh os installed.

Insist that they remove your drive while you wait. Take your old hard drive home and belt it with a hammer - several times. Or drill several holes through it.

It may still be possible to retrieve some of the information from your drive, but the time and equipment necessary is way beyond the capabilities/budget of the average data thief.

Unless you're, oh let's say an ex-secretary of state, performing a good wipe of the drive should be adequate (and a LiveCD or bootable USB stick with the applicable utility installed as described above fit for that purpose); the same for restoring old phones to factory settings. The time & resources necessary to recover data from such a device would be well beyond the capabilities (& interest level) of just about all except national actors. But you should be concerned about more than just your logon credentials. ANY PII (i.e., personally identifiable information), such as name, DOB, information about family members, addresses, SSNs, acct nos., phone nos., business/financial/legal documents, etc., if recovered, puts you at risk of identity theft, hijacked accounts, new accts created & loans taken out in your name, etc.

[IMA_FARANG]

If you are really worried there are commercial programs that will do a government approved certified high level clearing of data from a hard drive so iit can not be recovered that you can legally buy.

But be absolutely sure you really want to scrub that data from the drive......because once you do it that data is gone for good