You’re walking through a dark parking lot and think you’re being followed. Or your car goes off the road in a remote area and you can't reach your cell phone. What would you do? If you have a personal safety alarm, you already have the answer. A wide variety of gizmos can help keep you safe when you’re feeling vulnerable. Here are four.

Related: Don’t Be a Victim: Stay Safe in Parking Lots and Garages

Silent Beacon

silent beacon keychain

This is one of the newest personal safety alarms to hit the market. It’s a small keychain transponder with a panic button that communicates with your smartphone via its accompanying app and Bluetooth technology.

You indicate your emergency contacts during set-up. If you’d like your loved one(s) to get an alert when you’re in trouble, they’ll need to install the app as well. When you hit the emergency button, they’ll automatically receive a pop-up notification with your alert and exact whereabouts. The device can also be configured to call 911 or other emergency contacts. It doesn’t have a microphone of its own, so you can’t speak directly into it.

The keychain transponder is small, crushproof, waterproof, rechargeable and available in a variety of colors. Its indented button design prevents accidental alerts. This easy-to-access device has the potential to maximize personal safety in the event of a car accident, violent crime or injury ­— any circumstance where it would be difficult to reach for your phone. The downside is that it depends on being in close proximity to your functioning smartphone. It won’t work if your phone were to be lost, taken or out of service range.

Limited time offer of $60 for pre-orders; will be $99 retail. App is free and currently only available for iOS. Android coming soon.

(Photo: She Scribes)

Related: 6 Things Not to Do in an Emergency

ZOMM

zomm keychain

Like the Silent Beacon, ZOMM is a keychain device that works by communicating with your phone via Bluetooth. The unit is about the size of a poker chip and available in white, pink or black. It bills itself as a 3-in-1 combination of a panic alarm, one-touch 911 and a speakerphone. It also alerts you if you’re about to leave your phone behind. Use it as a siren to deter threats and help others find you, or use it to talk to 911 operators and other contacts without holding your phone.

ZOMM’s utility is not limited to smartphone users; it works with any phone that has Bluetooth integration. Using an expansion pack, you can use it as a hands-free speakerphone when you’re driving. But unlike the Silent Beacon, there’s no way to silently call for help, and ZOMM doesn’t provide location services.

Optional accompanying apps are available to help you change your ZOMM settings on the go. You also can change these settings on your computer.

Wireless Leash (for Android or any Bluetooth-enabled phone) $49.95

Wireless Leash Plus (for iPhone or any Bluetooth-enabled phone) $79.95

(Photo: theZomm)

SPOT Personal Tracker

spot personal tracker

If you want a portable tracking device that isn’t reliant on your phone, look no further than the SPOT Personal Tracker. This rugged pocket-sized instrument works almost anywhere because it communicates with GPS satellites, not a wireless network.

In addition to the transponder unit, you’ll need a service subscription, which starts at $14.99 per month. Basic functionalities include the “911” button, which sends your GPS location to the appropriate emergency services in the event of a life-threating situation, and the “Help” button, which is designated for non-life threatening emergencies. The “OK” button sends a pre-programmed message to your designated contacts, along with your location info. The service plan can be upgraded to include tools that track your progress and allow you to contact third-party towing professionals on the road or water.

SPOT is a great tool for hikers, sailors and other outdoor enthusiasts, but there are some environmental factors that could interfere with it. It requires a clear view of the sky, so it won’t be accurate indoors, in a cave or in very dense forests. You’ll also need to re-download the GPS almanac on a fairly regular basis for best results.

$99.99 MSRP, plus service subscription (required)

(Photo: Carzz)

Defendme Personal Alarm

Defendme is a relatively low-tech option with big potential impact. It’s a personal alarm, roughly the size of a USB flash drive, which you can clip onto your bag, zipper or keychain. When activated, it emits a loud 120-decibel siren that can be heard up to 300 feet away. This startling noise level is comparable to that of a thunderclap or a chainsaw.

Activating the alarm requires a firm tug on the attached lanyard. This pulls a D-shaped ring out of the unit; the sound begins when the ring is removed. To end the signal, simply click it back into place. The battery lasts for up to 30 minutes of alarm time or 6 months of standby time.

The simplicity of Defendme makes it a good choice when more advanced safety gadgets are out of reach or if you’d simply like a supplemental option.

$10

Related: 3 Self-Defense Moves Everyone Should Know

Michael Franco is a science and technology writer who secretly wishes he was an astronaut. His work has appeared in CNET, HowStuffWorks.com and Discover Magazine.