I was told God is everywhere, but not in the heart of the unbeliever?

That statement is getting at two different meanings of “God being present,” and people often mix them together.

God is everywhere — that’s His omnipresence.
Scripture is clear on this:

• “Where can I go from Your Spirit? … If I make my bed in hell, behold, You are there.” (Psalm 139:7–8)
  No one is outside God’s awareness, power, or authority — believer or unbeliever.

But when Christians say God is “in” someone’s heart, they’re talking about something more specific:
👉 God’s indwelling presence through the Holy Spirit.

The Bible teaches that:

• The Holy Spirit dwells in believers (John 14:16–17, Romans 8:9–10)

• This indwelling happens through faith in Christ, not just existence

Jesus said it plainly:

• “The world cannot receive Him… but you know Him, for He dwells with you and will be in you.” (John 14:17)

So here’s the clean way to say it, without confusion:

• God is everywhere — including around and aware of unbelievers

• God does not dwell in the heart of an unbeliever in the relational, saving, Spirit-indwelling sense

• An unbeliever is separated from God relationally, not geographically

A good analogy:

The sun shines everywhere, but not everyone opens the window.

God is present to all, but He only makes His home in those who receive Christ.