It makes me so happy to know that there are apps you can use to alert others and authorities in your area if anything goes wrong. Some good ones are listed below:

bSafe Personal Safety App (Android and IOS)
After you download this app, you choose a handful of 'guardians' this is your personal list of protectors who will be notified of your arrival at a destination and act as your lifeline if you're in trouble. With the gps feature enabled your guardians can track you at any time and if you tap the red SOS button on the app, a bright light shines on your phone and an alarm sounds, notifying your guardians. Your guardians, once contacted, call the police. Your phone even begins to record audio and video to use as a record for police later. It's all entirely free to anyone and I couldn't recommend it more.

Circle of 6 (Android and IOS)
This free app lets you easily and discretely communicate with 6 friends or family members of your choice to help you prevent violence before it happens
Press the car, phone, or chat icon when you need a helping hand and someone can pick you up, call you, or text you right away. The danger button gives you the options to call hotlines for either sexual or domestic abuse victims. This app is pretty helpful for if you're on a bad date or stuck at a party and need to be picked up.

Watch over Me (Android, IOS)

The paid version of Watch Over Me can send email, text, or Facebook alerts to your pre-selected emergency network if you're in trouble. It also has GPS tracking of your location and a "report crime" function. Set the phone to "watch over" you for a pre-determined amount of time or until you reach a specific location. If you don't check in when you should, the phone alerts the emergency contacts you select. The app can also notify you when you've entered an area perceived unsafe, so you can put your own instincts on high alert and get ready to use the app if necessary. If you're in danger, shake your phone to trigger an emergency alert and begin recording what is happening. The free app "watches over" you for five minutes, which is OK in some situations. But you get a longer time with the feature-rich premium version, which we think is well worth $9.99 for a 3-month subscription or $23.99 for a full year.

Kitestring (SMS-based)
For just $3/month, Kitestring checks in with you at pre-programmed times and alerts your selected network if you don't reply to the text message. This SMS-based service is easy to use and doesn't require a smartphone. It's better than relying on friends or family to manually ask for check-ins when you're on a blind date, a run, or in an unfamiliar place. The free plan provides eight check-ins per month and connects with one emergency contact, while the premium service offers unlimited contacts and unlimited check-ins, making it well worth the subscription fee.

Recommend some more in the comments below guys!