diff --git a/.luacheckrc b/.luacheckrc
index f6c991513..ab850f9bb 100644
--- a/.luacheckrc
+++ b/.luacheckrc
@@ -6,6 +6,9 @@ globals = {
 }
 
 read_globals = {
+    "ANDROID_FONT_DIR",
+    "KOBO_TOUCH_MIRRORED",
+    "KOBO_SYNC_BRIGHTNESS_WITH_NICKEL",
     "DRCOUNTMAX",
     "DHINTCOUNT",
     "DFULL_SCREEN",
diff --git a/.travis.yml b/.travis.yml
index fac1d94fd..a70d771b6 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -71,7 +71,7 @@ script:
   - make all
   - travis_retry make testfront
   - luajit $(which luacheck) --no-color -q frontend | tee ./luacheck.out
-  - test $(grep Total ./luacheck.out | awk '{print $2}') -le 140
+  - test $(grep Total ./luacheck.out | awk '{print $2}') -le 65
 
 after_success:
   - make coverage
diff --git a/frontend/apps/opdscatalog/opdscatalog.lua b/frontend/apps/opdscatalog/opdscatalog.lua
index f86de7e6e..50ec13910 100644
--- a/frontend/apps/opdscatalog/opdscatalog.lua
+++ b/frontend/apps/opdscatalog/opdscatalog.lua
@@ -1,21 +1,10 @@
 local InputContainer = require("ui/widget/container/inputcontainer")
 local FrameContainer = require("ui/widget/container/framecontainer")
-local FileManagerMenu = require("apps/filemanager/filemanagermenu")
-local DocumentRegistry = require("document/documentregistry")
-local VerticalGroup = require("ui/widget/verticalgroup")
-local ButtonDialog = require("ui/widget/buttondialog")
-local VerticalSpan = require("ui/widget/verticalspan")
 local OPDSBrowser = require("ui/widget/opdsbrowser")
-local TextWidget = require("ui/widget/textwidget")
-local lfs = require("libs/libkoreader-lfs")
 local UIManager = require("ui/uimanager")
-local Font = require("ui/font")
 local Screen = require("device").screen
-local Geom = require("ui/geometry")
-local Event = require("ui/event")
 local DEBUG = require("dbg")
 local _ = require("gettext")
-local util = require("ffi/util")
 local Blitbuffer = require("ffi/blitbuffer")
 
 local OPDSCatalog = InputContainer:extend{
diff --git a/frontend/apps/reader/modules/readerbookmark.lua b/frontend/apps/reader/modules/readerbookmark.lua
index c02f04cc5..55f30cc5e 100644
--- a/frontend/apps/reader/modules/readerbookmark.lua
+++ b/frontend/apps/reader/modules/readerbookmark.lua
@@ -92,7 +92,7 @@ function ReaderBookmark:importSavedHighlight(config)
     if not config:readSetting("highlights_imported") then
         for page, marks in pairs(textmarks) do
             for _, mark in ipairs(marks) do
-                local page = self.ui.document.info.has_pages and page or mark.pos0
+                page = self.ui.document.info.has_pages and page or mark.pos0
                 -- highlights saved by some old versions don't have pos0 field
                 -- we just ignore those highlights
                 if page then
@@ -125,7 +125,7 @@ function ReaderBookmark:onSaveSettings()
 end
 
 function ReaderBookmark:onToggleBookmark()
-    local pn_or_xp = nil
+    local pn_or_xp
     if self.ui.document.info.has_pages then
         pn_or_xp = self.view.state.page
     else
@@ -295,16 +295,16 @@ end
 
 -- binary search of sorted bookmarks
 function ReaderBookmark:isBookmarkAdded(item)
-    local _start, _middle, _end, direction = 1, 1, #self.bookmarks, 0
+    local _start, _middle, _end = 1, 1, #self.bookmarks
     while _start <= _end do
         _middle = math.floor((_start + _end)/2)
         if self:isBookmarkSame(item, self.bookmarks[_middle]) then
             return true
         end
         if self:isBookmarkInPageOrder(item, self.bookmarks[_middle]) then
-            _end, direction = _middle - 1, 0
+            _end = _middle - 1
         else
-            _start, direction = _middle + 1, 1
+            _start = _middle + 1
         end
     end
     return false
diff --git a/frontend/apps/reader/modules/readerrotation.lua b/frontend/apps/reader/modules/readerrotation.lua
index 30d32c358..4b8ead8cf 100644
--- a/frontend/apps/reader/modules/readerrotation.lua
+++ b/frontend/apps/reader/modules/readerrotation.lua
@@ -1,9 +1,6 @@
 local InputContainer = require("ui/widget/container/inputcontainer")
-local Screen = require("device").screen
-local Geom = require("ui/geometry")
 local Device = require("device")
 local Event = require("ui/event")
-local GestureRange = require("ui/gesturerange")
 local _ = require("gettext")
 
 local ReaderRotation = InputContainer:new{
@@ -26,7 +23,7 @@ function ReaderRotation:init()
     end
 end
 
--- TODO: reset rotation on new document, maybe on new page?
+-- @TODO: reset rotation on new document, maybe on new page?
 
 function ReaderRotation:onRotate(rotate_by)
     self.current_rotation = (self.current_rotation + rotate_by) % 360
diff --git a/frontend/apps/reader/modules/readersearch.lua b/frontend/apps/reader/modules/readersearch.lua
index a21aba836..af7274fab 100644
--- a/frontend/apps/reader/modules/readersearch.lua
+++ b/frontend/apps/reader/modules/readersearch.lua
@@ -1,8 +1,6 @@
 local InputContainer = require("ui/widget/container/inputcontainer")
 local ButtonDialog = require("ui/widget/buttondialog")
 local UIManager = require("ui/uimanager")
-local Geom = require("ui/geometry")
-local Screen = require("ui/screen")
 local DEBUG = require("dbg")
 local _ = require("gettext")
 
@@ -69,7 +67,7 @@ function ReaderSearch:onShowSearchDialog(text)
             self.ui.highlight:clear()
         end,
     }
-    local res = do_search(self.searchFromCurrent, text, 0)()
+    do_search(self.searchFromCurrent, text, 0)()
     UIManager:show(self.search_dialog)
     -- TODO: regional
     UIManager:setDirty(self.dialog, "partial")
diff --git a/frontend/device/android/device.lua b/frontend/device/android/device.lua
index 493f922ed..82c2bfc6b 100644
--- a/frontend/device/android/device.lua
+++ b/frontend/device/android/device.lua
@@ -1,5 +1,5 @@
 local Generic = require("device/generic/device")
-local isAndroid, android = pcall(require, "android")
+local _, android = pcall(require, "android")
 local ffi = require("ffi")
 local DEBUG = require("dbg")
 
diff --git a/frontend/device/generic/device.lua b/frontend/device/generic/device.lua
index 0f1aabfe6..79992c8e7 100644
--- a/frontend/device/generic/device.lua
+++ b/frontend/device/generic/device.lua
@@ -40,7 +40,7 @@ local Device = {
 }
 
 function Device:new(o)
-    local o = o or {}
+    o = o or {}
     setmetatable(o, self)
     self.__index = self
     return o
diff --git a/frontend/device/generic/powerd.lua b/frontend/device/generic/powerd.lua
index e8902061b..fc9476c0e 100644
--- a/frontend/device/generic/powerd.lua
+++ b/frontend/device/generic/powerd.lua
@@ -10,7 +10,7 @@ local BasePowerD = {
 }
 
 function BasePowerD:new(o)
-    local o = o or {}
+    o = o or {}
     setmetatable(o, self)
     self.__index = self
     if o.init then o:init() end
diff --git a/frontend/device/gesturedetector.lua b/frontend/device/gesturedetector.lua
index 59e1404fb..d3f46dbb6 100644
--- a/frontend/device/gesturedetector.lua
+++ b/frontend/device/gesturedetector.lua
@@ -73,7 +73,7 @@ local GestureDetector = {
 }
 
 function GestureDetector:new(o)
-    local o = o or {}
+    o = o or {}
     setmetatable(o, self)
     self.__index = self
     if o.init then o:init() end
diff --git a/frontend/device/input.lua b/frontend/device/input.lua
index 322a2ed4c..ae992777e 100644
--- a/frontend/device/input.lua
+++ b/frontend/device/input.lua
@@ -6,6 +6,8 @@ local _ = require("gettext")
 local Key = require("device/key")
 local GestureDetector = require("device/gesturedetector")
 
+-- luacheck: push
+-- luacheck: ignore
 -- constants from <linux/input.h>
 local EV_SYN = 0
 local EV_KEY = 1
@@ -36,6 +38,7 @@ local ABS_MT_POSITION_X = 53
 local ABS_MT_POSITION_Y = 54
 local ABS_MT_TRACKING_ID = 57
 local ABS_MT_PRESSURE = 58
+-- luacheck: pop
 
 --[[
 an interface to get input events
@@ -105,7 +108,7 @@ local Input = {
 }
 
 function Input:new(o)
-    local o = o or {}
+    o = o or {}
     setmetatable(o, self)
     self.__index = self
     if o.init then o:init() end
diff --git a/frontend/device/kindle/device.lua b/frontend/device/kindle/device.lua
index 6429c0928..dae72a4e8 100644
--- a/frontend/device/kindle/device.lua
+++ b/frontend/device/kindle/device.lua
@@ -147,8 +147,11 @@ function Kindle4:init()
     Kindle.init(self)
 end
 
+-- luacheck: push
+-- luacheck: ignore
 local ABS_MT_POSITION_X = 53
 local ABS_MT_POSITION_Y = 54
+-- luacheck: pop
 function KindleTouch:init()
     self.screen = require("ffi/framebuffer_mxcfb"):new{device = self, debug = DEBUG}
     self.powerd = require("device/kindle/powerd"):new{
diff --git a/frontend/device/pocketbook/device.lua b/frontend/device/pocketbook/device.lua
index e33a4c4ca..14d64fd03 100644
--- a/frontend/device/pocketbook/device.lua
+++ b/frontend/device/pocketbook/device.lua
@@ -1,6 +1,8 @@
 local Generic = require("device/generic/device") -- <= look at this file!
 local DEBUG = require("dbg")
 
+-- luacheck: push
+-- luacheck: ignore
 local EVT_INIT = 21
 local EVT_EXIT = 22
 local EVT_SHOW = 23
@@ -32,6 +34,7 @@ local KEY_PREV2  = 0x1c
 local KEY_NEXT2  = 0x1d
 local KEY_COVEROPEN	= 0x02
 local KEY_COVERCLOSE	= 0x03
+-- luacheck: pop
 
 local function yes() return true end
 
@@ -49,12 +52,12 @@ function PocketBook:init()
             ev.value = ev.type == EVT_KEYDOWN and 1 or 0
             ev.type = 1 -- EV_KEY
         elseif ev.type == EVT_BACKGROUND then
-            isInBackGround = true
+            self.isInBackGround = true
             self:onPowerEvent("Power")
-        elseif isInBackGround and ev.type == EVT_FOREGROUND then
-            isInBackGround = false
+        elseif self.isInBackGround and ev.type == EVT_FOREGROUND then
+            self.isInBackGround = false
             self:onPowerEvent("Power")
-        elseif not isInBackGround and ev.type == EVT_FOREGROUND then
+        elseif not self.isInBackGround and ev.type == EVT_FOREGROUND then
             self.screen:refreshPartial()
         end
     end)
diff --git a/frontend/document/koptinterface.lua b/frontend/document/koptinterface.lua
index dd5046071..1b10fcbea 100644
--- a/frontend/document/koptinterface.lua
+++ b/frontend/document/koptinterface.lua
@@ -594,7 +594,7 @@ function KoptInterface:getReflewOCRWord(doc, pageno, rect)
         local cached = Cache:check(kctx_hash)
         if cached then
             local kc = self:waitForContext(cached.kctx)
-            local ok, word = pcall(
+            local _, word = pcall(
                 kc.getTOCRWord, kc, "dst",
                 rect.x, rect.y, rect.w, rect.h,
                 self.tessocr_data, self.ocr_lang, self.ocr_type, 0, 1)
@@ -628,7 +628,7 @@ function KoptInterface:getNativeOCRWord(doc, pageno, rect)
         --kc:exportSrcPNGFile({rect}, nil, "ocr-word.png")
         local word_w, word_h = kc:getPageDim()
         --DEBUG(word_w, word_h)
-        local ok, word = pcall(
+        local _, word = pcall(
             kc.getTOCRWord, kc, "src",
             0, 0, word_w, word_h,
             self.tessocr_data, self.ocr_lang, self.ocr_type, 0, 1)
@@ -655,7 +655,7 @@ end
 function KoptInterface:getClipPageContext(doc, pos0, pos1, pboxes, drawer)
     assert(pos0.page == pos1.page)
     assert(pos0.zoom == pos1.zoom)
-    local rect = nil
+    local rect
     if pboxes and #pboxes > 0 then
         local box = pboxes[1]
         rect = Geom:new{
@@ -1060,7 +1060,7 @@ function KoptInterface:nativeToPageRectTransform(doc, pageno, rect)
             y = rect.y + rect.h - 5
         }
         local boxes = self:getPageBoxesFromPositions(doc, pageno, pos0, pos1)
-        res_rect = nil
+        local res_rect = nil
         if #boxes > 0 then
             res_rect = boxes[1]
             for _, box in pairs(boxes) do
diff --git a/frontend/ui/uimanager.lua b/frontend/ui/uimanager.lua
index 48e693310..04836ab33 100644
--- a/frontend/ui/uimanager.lua
+++ b/frontend/ui/uimanager.lua
@@ -422,7 +422,7 @@ function UIManager:_refresh(mode, region)
             -- combine both refreshes' regions
             local combined = region:combine(self._refresh_stack[i].region)
             -- update the mode, if needed
-            local mode = update_mode(mode, self._refresh_stack[i].mode)
+            mode = update_mode(mode, self._refresh_stack[i].mode)
             -- remove colliding update
             table.remove(self._refresh_stack, i)
             -- and try again with combined data