Tried and tested as it may be, the traditional lock-and-key system has its shortcomings. Keys can then get lost or stolen, and if they fall into the wrong hands, your only choice is to change your locks. Anyone with a key can come and go as they please, even if you only wanted to grant access for a specific purpose or a limited time. And you need to have a copy of the key made by a professional to give someone ongoing access to your home.

However, several options are emerging for changing your current deadbolt into one that can be conveniently operated via smartphone and afford you more thorough control over access to your property. Most of these systems have three main components: an electronic deadbolt, an encrypted smartphone application by which to operate it and some type of fob for entry without smartphones. We found five different “smart lock” systems and compared their security, accessibility and operational features.

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Kevo ($219; iOS & Android, with some limitations)

Kevo is a well-supported, award-winning system. The starter package comes with one deadbolt, a door-mounted interior unit, batteries, two eKeys, one fob and two traditional keys.

In most doors, installation requires only a Philips head screwdriver and 4 AA batteries (included). To program the deadbolt, the owner utilizes the Kevo app via his smartphone. The owner distributes “eKeys” to visitors via the app (they can be purchased for $1.99 each). The eKeys can be programmed to allow unrestricted anytime access or only under pre-set time constraints. They never expire, and can be revoked and reassigned from individuals as needed. Owners can distribute an unlimited amount of Guest eKeys for free, which expire after 24 hours.

What makes Kevo stand out is just how easy it is for eKey holders to unlock the door. Anyone with an eKey — as long as they have a Kevo app-equipped smartphone or the alternative fob — can unlock the door simply by touching the lock with their fingertips. The device can stay in a purse or pocket thanks to Bluetooth technology. The app runs in the background, which means you don’t need to make sure it’s on ahead of time.

If your phone dies, you can either use the Bluetooth fob, a traditional metal key or sign into the Kevo app on any other supported smartphone. Your eKey will automatically be transferred. Because it can accept traditional keys, the Kevo deadbolt has a very traditional style that won’t look out of place in your décor.

The Kevo app also keeps track of who unlocks/locks your home and when. It records who accepts eKeys and when users are allowed access. However, this system is reliant on reliable wireless Internet service in your home. In the event of a lost connection, scheduled and guest eKeys can lose access.

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August Smart Lock ($249.99; iOS or Android)

Like Kevo, August boasts an easy-to-install electronic deadbolt that fits easily in most exterior doors. The August door unit is comparatively sleek, though still low profile.

August lets the homeowner distribute an unlimited amount of "invitations," which can be programmed for anytime access or scheduled entry only. These virtual keys can be used by anyone with a smartphone that supports the August app. The August lock replaces the inside portion of a traditional deadbolt — there is no need to change the outside. It runs on four AA batteries so it works even if the WiFi or power goes out.

August can give the homeowner remote control over their locks and home security with the additional purchase of an August Connect unit ($49.99). The Connect must be plugged into an outlet within 15 to 30 feet of each electronic deadbolt. Once set up, it allows the homeowner to lock and unlock the door remotely and receive instant notifications when anyone uses a virtual key. The Connect utilizes the home’s power and WiFi connection, so it won’t work in the event of an outage.

If visitors don’t have a smartphone, or if there is a total power outage, August also can be operated with an ordinary metal key.

Goji ($278; iOS or Android)

This is a brand-new option hitting the market in 2015. It differentiates itself with the sleek LED screen on its lock and unique remote alert system. It can send the owner real-time picture alerts, via text or email, of each person accessing the home.

Goji does not require a WiFi connection to validate your visitor’s entry. However, WiFi is necessary for tracking and alert features. The Goji deadlock can be operated via smartphone or fob (an additional $40 each). It also includes traditional key backups, a 24-7 support hotline and a network of approved locksmiths should you need professional assistance.

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Ok-i-Dokeys ($199, iOS or Android)

This system is perhaps the most expandable and customizable of today’s smart lock options. It installs right on top of any existing deadbolt with an interior latch-style lock, so you can continue using your current key even after the system is in in place.

Ok-i-Dokeys can start with just one electronic deadbolt that can be operated via Bluetooth-enabled smartphone. Or, you can add on locks for your garage and exterior gates, and manage it all remotely with the purchase of a Smart Gateway that utilizes your home wireless network. With an optional Smart-Reader ($99.99) accessibility can be granted to cell phones, wristbands, fobs or keycards. These options do not require wireless connectivity.

Homeowners also have optional hands-free settings and intruder alerts with Ok-i-Dokeys. One caveat: The plastic-exterior gadgets in the Ok-i-Dokeys arsenal are arguably less attractive than those of its competitors. This downside becomes more apparent as you extend your system.

Yale 2 You Mobile Phone Entry ($224.99, Android only)

This is the newest offering from Yale, one of the oldest international lock brands. Unlike the other offerings covered here, it has no keyhole. Access is granted via Android device or by entering an access code into the touch-screen keypad.

The owner can distribute and retrieve up to 10 digital keys via the accompanying app. Owners can monitor access history and get alerts whenever someone enters or exits. They also can set up access codes that can be entered manually by visitors without an Android device.

Due to its keypad, the exterior unit is relatively large (2 3/4" wide x 5 1/2" tall), so it will have a visual impact on your entry door. It is available in a nickel, brass or oil-rubbed bronze finish.

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.

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