diff --git a/.gitignore b/.gitignore
index aae6e56..11d8cc2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,3 @@
 *.db
-db.json
 tmp.*
 *.log
diff --git a/dev.fish b/dev.fish
index 0bd37db..07615e5 100644
--- a/dev.fish
+++ b/dev.fish
@@ -3,9 +3,6 @@ set oldsum (cat (find . \( -name '*.rb' -o -name '*.js' \) | sort) | md5sum)
 if not test -e infinsweeper.db
   sqlite3 infinsweeper.db < schema.sql
 end
-if not test -e db.json
-  echo "{\"account_num\":0,\"pass_num\":0,\"signed_in_users\":{}}" > db.json
-end
 pkill ruby
 ruby main.rb -p8080 &
 echo "" > $pipe_path
diff --git a/main.rb b/main.rb
index b15bfee..2448fca 100644
--- a/main.rb
+++ b/main.rb
@@ -4,8 +4,38 @@ require "json"
 require_relative "players"
 require_relative "session"
 
-json_path = File.expand_path("db.json")
-signed_in_users = JSON.parse(File.read(json_path))["signed_in_users"]
+ALPHANUM = [*"0".."9", *"A".."Z", *"a".."z", "-", "_"].freeze
+
+db_file = File.expand_path("infinsweeper.db")
+DB = Sequel.connect("sqlite:///#{db_file}", single_threaded: false)
+DB.run("PRAGMA foreign_keys = ON;")
+
+signed_in_users = DB[:SignedInUsers].all.map { |x| [x[:code], x[:player]] }.to_h
+
+Thread.new do
+  loop do
+    now = Time.now
+    fifteen_days_ago = now - (60 * 60 * 24 * 15)
+    six_days_ago = now - (60 * 60 * 24 * 6)
+    old_sessions = (DB[:SignedInUsers].where { created_at < fifteen_days_ago }.all +
+                    DB[:SignedInUsers].where { last_used_at < six_days_ago }.all).uniq { |s| s[:code] }
+    old_sessions.each do |session|
+      begin
+        DB[:SignedInUsers].where(code: session[:code]).delete
+      rescue StandardError => e
+        File.write("log/main.log",
+                   "[#{Time.now}] Thread DB error: #{e.message} on #{session[:code]} for #{session[:player]}\n",
+                   mode: "a")
+      end
+      signed_in_users.delete(session[:code])
+      puts "Auto-logged out: #{session[:player]} (expired session)"
+    end
+  rescue StandardError => e
+    File.write("log/main.log", "[#{Time.now}] Thread error: #{e.message}\n", mode: "a")
+  ensure
+    sleep 60 * 60 * 24
+  end
+end
 
 set :public_folder, "public"
 
@@ -21,37 +51,35 @@ post "/new_player" do
   data = JSON.parse(request.body.read)
   if data["email"].nil? || data["pass"].nil? || data["username"].nil?
     status 400
-    return '{"message": "Bad request made!"}'
+    return { "message" => "Bad request made!" }.to_json
   end
   player = Players.mk_player(data["username"], data["email"], data["pass"])
   case player
   when "Successfully registered!"
-    hash = XXhash.xxh64(data["email"] + Time.now.to_s, 1234)
-    code = ""
-    while hash.positive?
-      code << ALPHANUM[hash % 64]
-      hash /= 64
-    end
-    code = code.reverse.rjust(12, "0")
-    set_session(request, response, "user", code)
+    code = Array.new(24) { ALPHANUM.sample }.join
+    set_session(request, response, "user", code, code)
     signed_in_users[code] = data["email"]
-    json = JSON.parse(File.read(json_path))
-    json["signed_in_users"] = signed_in_users.clone
-    File.write(json_path, JSON.pretty_generate(json))
+    begin
+      DB["insert into SignedInUsers (code, player) values (?, ?)", code, data["email"]].insert
+    rescue Sequel::Error => e
+      File.write("log/main.log", "DB Error: #{e.message}\n", mode: "a")
+      status 500
+      return { "message" => "Internal server error when signing you in!" }.to_json
+    end
     status 200
   else
     status 400
   end
-  return "{\"message\": \"#{player}\"}"
+  return { "message" => player }.to_json
 end
 
 get "/verify/:code" do
   if Players.verify(params[:code])
     status 200
-    return "{\"message\": \"Verified successfully!\"}"
+    return { "message" => "Verified successfully!" }.to_json
   else
     status 400
-    return "{\"message\": \"Used or Invalid code!\"}"
+    return { "message" => "Couldn't verify!" }
   end
 end
 
@@ -59,24 +87,22 @@ post "/login" do
   data = JSON.parse(request.body.read)
   player = Players.authorized?(data["email"], data["pass"])
   if player
-    hash = XXhash.xxh64(data["email"] + Time.now.to_s, 1234)
-    code = ""
-    while hash.positive?
-      code << ALPHANUM[hash % 64]
-      hash /= 64
-    end
-    code = code.reverse.rjust(12, "0")
-    set_session(request, response, "user", code)
+    code = Array.new(24) { ALPHANUM.sample }.join
+    set_session(request, response, "user", code, code)
     signed_in_users[code] = data["email"]
-    json = JSON.parse(File.read(json_path))
-    json["signed_in_users"] = signed_in_users.clone
-    File.write(json_path, JSON.pretty_generate(json))
+    begin
+      DB["insert into SignedInUsers (code, player) values (?, ?)", code, data["email"]].insert
+    rescue Sequel::Error => e
+      File.write("log/main.log", "DB Error: #{e.message}\n", mode: "a")
+      status 500
+      return { "message" => "Internal server error when signing you in!" }.to_json
+    end
     status 200
-    return "{\"message\": \"Remember to verify your email!\"}" unless Players.verified?(data["email"])
-    return "{\"message\": \"Signed in successfully!\"}"
+    return { "message" => "Remember to verify your email!" }.to_json unless Players.verified?(data["email"])
+    return { "message" => "Signed in successfully!" }.to_json
   else
     status 400
-    return "{\"message\": \"Email or password incorrect!\"}"
+    return { "message" => "Couldn't sign you in!" }.to_json
   end
 end
 
@@ -84,40 +110,44 @@ post "/logout" do
   uid = get_session(request, response, "user")
   if signed_in_users[uid].nil?
     status 400
-    return "{\"message\":\"Not signed in!\"}"
+    return { "message" => "Not signed in!" }.to_json
   end
   signed_in_users.delete(uid)
   rm_session(request, response, "user")
-  json = JSON.parse(File.read(json_path))
-  json["signed_in_users"] = signed_in_users.clone
-  File.write(json_path, JSON.pretty_generate(json))
+  begin
+    DB["delete from SignedInUsers where code = ?", uid].delete
+  rescue Sequel::Error => e
+    File.write("log/main.log", "DB Error: #{e.message}\n", mode: "a")
+    status 500
+    return { "message" => "Internal server error when signing you out!" }.to_json
+  end
   status 200
-  return "{\"message\":\"Signed out!\"}"
+  return { "message" => "Signed out successfully!" }.to_json
 end
 
 post "/forgot_password" do
   data = JSON.parse(request.body.read)
   if data["email"].nil?
     status 400
-    return "{\"message\":\"Bad request made!\"}"
+    return { "message" => "Bad request made (Email not provided)!" }.to_json
   end
   Players.pass_req(data["email"])
   status 200
-  return "{\"message\":\"Password reset email sent!\"}"
+  return { "message" => "Email sent successfully!" }.to_json
 end
 
 post "/reset_password/:code" do
   data = JSON.parse(request.body.read)
   if data["pass"].nil? || params[:code].nil?
     status 400
-    return "{\"message\":\"Bad request made!\"}"
+    return { "message" => "Bad request made!" }.to_json
   end
   if Players.pass_reset(data["pass"], params[:code])
     status 200
-    return "{\"message\":\"Password reset successfully!\"}"
+    return { "message" => "Password reset successfully!" }.to_json
   else
     status 400
-    return "{\"message\":\"Couldn\'t reset password!\"}"
+    return { "message" => "Couldn't reset password!" }.to_json
   end
 end
 
@@ -125,18 +155,15 @@ delete "/rm_player" do
   uid = get_session(request, response, "user")
   if uid.nil? || signed_in_users[uid].nil?
     status 400
-    return '{"message": "Not signed in!"}'
+    return { "message" => "Not signed in!" }.to_json
   end
   if Players.rm_player(signed_in_users[uid])
-    status 200
     signed_in_users.delete(uid)
     rm_session(request, response, "user")
-    json = JSON.parse(File.read(json_path))
-    json["signed_in_users"] = signed_in_users.clone
-    File.write(json_path, JSON.pretty_generate(json))
-    return '{"message": "Sorry to see you go.."}'
+    status 200
+    return { "message" => "Sorry to see you go.." }.to_json
   else
     status 500
-    return '{"message": "Couldn\'t delete!"}'
+    return { "message" => "Couldn't delete!" }.to_json
   end
 end
diff --git a/players.rb b/players.rb
index 5cd23e0..4b33596 100644
--- a/players.rb
+++ b/players.rb
@@ -8,6 +8,7 @@ ALPHANUM = [*"0".."9", *"A".."Z", *"a".."z", "-", "_"].freeze
 module Players
   db_file = File.expand_path("infinsweeper.db")
   DB = Sequel.connect("sqlite:///#{db_file}", single_threaded: false)
+  DB.run("PRAGMA foreign_keys = ON;")
 
   def self.list
     DB["select * from Players"].all
@@ -26,19 +27,7 @@ module Players
 
     digest = XXhash.xxh32(pass, 1234)
 
-    path = File.expand_path("db.json")
-    json = File.exist?(path) ? JSON.parse(File.read(path)) : {}
-    json["account_num"] ||= 0
-    account_num = json["account_num"]
-    json["account_num"] += 1
-    File.write(path, JSON.pretty_generate(json))
-    account_num = XXhash.xxh64(account_num, 1234)
-    code = ""
-    while account_num.positive?
-      code << ALPHANUM[account_num % 64]
-      account_num /= 64
-    end
-    code = code.reverse.rjust(12, "0")
+    code = Array.new(24) { ALPHANUM.sample }.join
 
     DB[
       "insert into Players (email, digest, username, activation_code) values (?, ?, ?, ?)",
@@ -64,20 +53,8 @@ module Players
 
   def self.pass_req(email)
     return unless self[email]
-    path = File.expand_path("db.json")
-    json = File.exist?(path) ? JSON.parse(File.read(path)) : {}
-    json["pass_num"] ||= 0
-    pass_num = json["pass_num"]
-    json["pass_num"] += 1
-    File.write(path, JSON.pretty_generate(json))
-    pass_num = XXhash.xxh64(pass_num, 1234)
-    code = ""
-    while pass_num.positive?
-      code << ALPHANUM[pass_num % 64]
-      pass_num /= 64
-    end
-    code = code.reverse.rjust(12, "0")
 
+    code = Array.new(24) { ALPHANUM.sample }.join
     DB["update Players set new_pass_code = ? where email = ?", code, email].update
 
     send_email(:pass_req, email, code)
@@ -108,9 +85,14 @@ module Players
   end
 
   Thread.new do
-    sleep 60 * 60
-    unverified.each do |player|
-      rm_player(player[:email]) if player[:created_at] + 24 * 60 * 60 < Time.now
+    loop do
+      unverified.each do |player|
+        rm_player(player[:email]) if player[:created_at] + 24 * 60 * 60 < Time.now
+      end
+    rescue StandardError => e
+      File.write("log/main.log", "Thread error: #{e.message}\n", mode: "a")
+    ensure
+      sleep 60 * 60
     end
   end
 end
diff --git a/schema.sql b/schema.sql
index 3decd50..e0e1cc6 100644
--- a/schema.sql
+++ b/schema.sql
@@ -1,4 +1,4 @@
-CREATE TABLE Players (
+CREATE TABLE IF NOT EXISTS Players (
   email TEXT PRIMARY KEY,
   username TEXT UNIQUE,
   digest BLOB,
@@ -7,3 +7,11 @@ CREATE TABLE Players (
   new_pass_code TEXT,
   created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
 );
+
+CREATE TABLE IF NOT EXISTS SignedInUsers (
+  code TEXT PRIMARY KEY,
+  player TEXT,
+  created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+  last_used_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+  FOREIGN KEY (player) REFERENCES Players (email) ON DELETE CASCADE
+);