The iPhone has been on the market since 2007, yet it still hides many secrets. Want to obscure your number when calling someone? Just input a simple code and you’ll become anonymous. Or what about the infamous *#21#?

If you’re a developer or die-hard iPhone user, chances are you’ve known about these codes for a while. For the rest of us, inputting these codes into your iPhone’s dialer might make for a neat party trick. I don’t know how useful these settings are for daily use, but they’re there in case you ever want to open a “field mode” on your device. Why not?

None of these “interrogation” codes are all that impressive, but it’s still fun to look behind the curtain and feel like you’re uncovering your device’s darkest secrets. The codes below should work regardless of what iPhone you currently have, and regardless of carrier. If you’re feeling especially curious one afternoon, check out the list below.

Secret iPhone codes:

IMEI number: *#06#

Want to know your device’s unique 15-digit IMEI code? This is the easiest way to find out.

Field test: *3001#12345#

Get live updated information about your cell network, and see the numerical value of your signal.

Call barring: *#33# / *33*pin# / #33*pin#

This allows you to block or unblock outgoing calls.

Call waiting: *#43# / *43# / #43#

A more cumbersome way to see if you have call waiting enabled. The same settings are available in Settings.

Call forwarding: *#21#

Yet another more difficult way to see if call forwarding is enabled. You can tweak this Settings already.

Become anonymous: #31#

Perhaps the most useful one on the list, this one allows users to hide their number when calling someone. Another feature that can also be accessed in Settings.

Text message center: *#5005*7672# + Call

If you ever get the urge to check your carrier’s text message center number.

EFR mode: *3370# + Call

Apparently improved voice quality for GSM conversations.

Display available minutes: *646#

Pretty self-explanatory.

Check bill balance: *225#

Also self-explanatory.

Check number of missed calls: *3282#