diff --git a/lib/guard/listener.rb b/lib/guard/listener.rb
index e1df894..9ea5948 100644
--- a/lib/guard/listener.rb
+++ b/lib/guard/listener.rb
@@ -8,7 +8,7 @@ module Guard
   autoload :Polling, 'guard/listeners/polling'
 
   class Listener
-    attr_reader :last_event
+    attr_reader :last_event, :sha1_checksums_hash
 
     def self.select_and_init
       if mac? && Darwin.usable?
@@ -24,6 +24,7 @@ module Guard
     end
 
     def initialize
+      @sha1_checksums_hash = {}
       update_last_event
     end
 
@@ -32,7 +33,7 @@ module Guard
     end
 
     def modified_files(dirs, options = {})
-      files = potentially_modified_files(dirs, options).select { |path| File.file?(path) && recent_file?(path) }
+      files = potentially_modified_files(dirs, options).select { |path| File.file?(path) && file_modified?(path) && file_content_modified?(path) }
       files.map! { |file| file.gsub("#{Dir.pwd}/", '') }
     end
 
@@ -43,12 +44,24 @@ module Guard
       Dir.glob(dirs.map { |dir| "#{dir}#{match}" })
     end
 
-    def recent_file?(file)
-      File.mtime(file) >= last_event
+    def file_modified?(path)
+      # Depending on the filesystem, mtime is probably only precise to the second, so round
+      # both values down to the second for the comparison.
+      File.mtime(path).to_i >= last_event.to_i
     rescue
       false
     end
 
+    def file_content_modified?(path)
+      sha1_checksum = Digest::SHA1.file(path).to_s
+      if sha1_checksums_hash[path] != sha1_checksum
+        @sha1_checksums_hash[path] = sha1_checksum
+        true
+      else
+        false
+      end
+    end
+
     def self.mac?
       Config::CONFIG['target_os'] =~ /darwin/i
     end
diff --git a/spec/guard/listener_spec.rb b/spec/guard/listener_spec.rb
index 5d09104..5a62f43 100644
--- a/spec/guard/listener_spec.rb
+++ b/spec/guard/listener_spec.rb
@@ -35,7 +35,7 @@ describe Guard::Listener do
     it "updates last_event with time.now" do
       time = Time.now
       subject.update_last_event
-      subject.last_event.should >= time
+      subject.last_event.to_i.should >= time.to_i
     end
 
   end