Field Test for iPhone Signal Strength Returns in iOS 4.1

Archived from Mac Observer.

When Apple released iOS 4.1 for iPhone Wednesday, the company once again included a utility that allows you to measure your signal strength on your device, a utility that that had been available before the release of iOS 4, but was not included when iOS 4 was introduced earlier this year.

The utility is called Field Test, and it is accessed by dialing *3001#12345#* (followed by the “Call” button). When you do that, a blank “page” launches with a title bar that reads “Field Test,” along with a Refresh button, as you can see in the image below. The Field Test part is that your signal bars will be replaced with a negative number that measures signal strength as expressed in decibels of noise in the signal.

To that end, the higher the number, the stronger the signal. -80db would represent a stronger signal than -90db, and -102db would be worse still (for instance, this reporter has particularly foul coverage at his office). TMO staff around the country found signal strengths ranging from -82db to about -120db, with any number lower than that representing little or no practical signal.

From user posts at Gizmodo, which first noted the return of Field Test, any Field Test near -70db represents something close to full signal strength. One staff member with an AT&T 3G Microcell got a measurement of -67db from one meter away from his microcell.

Pressing the Home button on your iPhone will end the Field Test and return your display to normal. Locking your phone (or allowing it to self-lock) with the Field Test still running will leave the Field Test numbers in your menu bar until you come back and quit the app via the Home button.


Tips on how to prolong your laptop battery life

This applies to any device that uses lithium ion batteries (i.e. laptops, smartphones).


  1. For lithium ion batteries, you do not need to discharge them fully and recharge constantly. Since they don’t have the same "memory" as older nickel-metal hydride batteries, it is actually better to discharge a lithium ion only partially (10 to 20%) before recharging. You need to do a full discharge only about every 30 charges (usually around every 2 to 3 weeks).
  2. Consider taking your battery out when using your laptop plugged into AC power. Just make sure to keep the contacts clean. If you need to clean them, use a lint-free cloth moistened with rubbing alcohol every couple of months.

Software & Hardware

  1. Defrag your hard drive regularly
  2. Dim your screen to the lowest level you can tolerate
  3. Close unused programs running in the background
  4. Disable WIFI when not in use.
  5. Hibernate your computer, not standby.


  1. Avoid propping your laptop on a pillow, blanket, or other soft surface that can heat up or block cooling fans.
  2. Clean your desk. It sounds strange, but if you have a dusty, dirty desk, that dust will get into the vents and clog the cooling fan. Once the dust is inside your laptop, it is much harder to remove. You can try blasting it out with canned air, but you run the risk of damaging internal components. You can also remove the vent and clean out the grit, but remember that taking apart your laptop can void the warranty. So clean your desk at least once a week, if not daily.
  3. Try not to store your laptop in a place where the air temperature exceeds 80 degrees Fahrenheit, such as a hot car or an outdoor patio. And if your laptop heats up or is cold, let it return to room temperature before starting up.
  4. Use a cooling pad when using a notebook computer on your lap.