US Automatic Sentry 300
#5 in Single swingFull review
A commercial grade, UL 325 listed single gate opener with a long warranty for buyers who value proven parts support over capacity per dollar.
Amazon $1,395$1,395
The US Automatic Sentry 300 is the better automatic gate opener overall, rated 3.2 to 3.0. The US Automatic Sentry 300 leads on warranty, gate length and gate weight. The Mighty Mule MM271 wins on price. The Mighty Mule MM271 costs $1,132.01 less ($262.99 vs $1,395).
Mighty Mule MM271
#7 in Single swingFull review
A budget, UL 325 listed kit for a short, light single gate. Anything over 12 ft or 300 lb needs the MM371W or larger.
Amazon $262.99$262.99
Prices were last checked November 2, 2026 and are subject to change; the price and availability shown by the retailer at the time of purchase apply.
Which should you buy?
- Choose the US Automatic Sentry 300 for warranty (3-year warranty vs 1-year warranty), gate length (gates up to 20 ft per leaf vs gates up to 12 ft per leaf) and gate weight (gates up to 400 lb per leaf vs gates up to 300 lb per leaf).
- Choose the Mighty Mule MM271 for price ($262.99 vs $1,395).
Scores side by side
Each factor is scored 0-100 against the same fixed reference points for every single swing automatic gate opener; a clear win is highlighted. How we rank explains each one.
| Factor weight | US Automatic Sentry 300 | Mighty Mule MM271 |
|---|---|---|
| Overall rating | 3.2/5 | 3.0/5 |
| Gate weight 20% | 24 gates up to 400 lb per leaf | 0 gates up to 300 lb per leaf |
| Gate length 15% | 100 gates up to 20 ft per leaf | 20 gates up to 12 ft per leaf |
| Safety listing 15% | 100 UL 325 listed | 100 UL 325 listed |
| Price 25% | 0 $1,395 | 96 $262.99 |
| Warranty 25% | 50 3-year warranty | 0 1-year warranty |
Specifications
| US Automatic Sentry 300 | Mighty Mule MM271 | |
|---|---|---|
| Gate | ||
| Gate type | Single swing | Single swing |
| Heaviest gate | 400 lb | 300 lb |
| Longest gate | 20 ft | 12 ft |
| Time to open | 16 s | 18 s |
| UL 325 listed | Yes | Yes |
| Power | ||
| Power | Battery, solar ready | Battery, solar ready |
| Motor voltage | 12 V | 12 V |
| Build | ||
| Remotes included | 2 | 1 |
| Weight | - | 16 lb |
| Warranty | 3 years | 1 year |